diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index e3ee7ea..7379bc3 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -3,7 +3,7 @@
   <component name="ChangeListManager">
     <list default="true" id="e7c9c2bb-66f1-4e37-904c-d33d8c113bde" name="Default" comment="">
       <change type="MODIFICATION" beforePath="$PROJECT_DIR$/.idea/workspace.xml" afterPath="$PROJECT_DIR$/.idea/workspace.xml" />
-      <change type="MODIFICATION" beforePath="$PROJECT_DIR$/js/dialogs/ImportPanel.js" afterPath="$PROJECT_DIR$/js/dialogs/ImportPanel.js" />
+      <change type="MODIFICATION" beforePath="$PROJECT_DIR$/php/module.calendar.php" afterPath="$PROJECT_DIR$/php/module.calendar.php" />
     </list>
     <ignored path="calendarimporter.iws" />
     <ignored path=".idea/workspace.xml" />
@@ -23,34 +23,12 @@
     <favorites_list name="calendarimporter" />
   </component>
   <component name="FileEditorManager">
-    <leaf SIDE_TABS_SIZE_LIMIT_KEY="300">
-      <file leaf-file-name="plugin.calendarimporter.js" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/js/plugin.calendarimporter.js">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="610">
-              <caret line="91" column="27" selection-start-line="91" selection-start-column="27" selection-end-line="91" selection-end-column="27" />
-              <folding />
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="upload.php" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/php/upload.php">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="408">
-              <caret line="34" column="0" selection-start-line="34" selection-start-column="0" selection-end-line="39" selection-end-column="1" />
-              <folding>
-                <element signature="e#6#905#0#PHP" expanded="true" />
-              </folding>
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="module.calendar.php" pinned="false" current-in-tab="false">
+    <leaf>
+      <file leaf-file-name="module.calendar.php" pinned="false" current-in-tab="true">
         <entry file="file://$PROJECT_DIR$/php/module.calendar.php">
           <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="260">
-              <caret line="231" column="30" selection-start-line="231" selection-start-column="25" selection-end-line="231" selection-end-column="30" />
+            <state relative-caret-position="279">
+              <caret line="691" column="13" selection-start-line="691" selection-start-column="13" selection-end-line="691" selection-end-column="13" />
               <folding>
                 <element signature="e#6#914#0#PHP" expanded="true" />
                 <element signature="e#1004#1022#0#PHP" expanded="true" />
@@ -59,40 +37,6 @@
           </provider>
         </entry>
       </file>
-      <file leaf-file-name="Actions.js" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/js/data/Actions.js">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="268">
-              <caret line="173" column="35" selection-start-line="173" selection-start-column="35" selection-end-line="173" selection-end-column="80" />
-              <folding />
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="ImportPanel.js" pinned="false" current-in-tab="true">
-        <entry file="file://$PROJECT_DIR$/js/dialogs/ImportPanel.js">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="583">
-              <caret line="113" column="29" selection-start-line="113" selection-start-column="21" selection-end-line="113" selection-end-column="29" />
-              <folding>
-                <element signature="n#!!doc" expanded="true" />
-              </folding>
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="helper.php" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/php/helper.php">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="407">
-              <caret line="41" column="15" selection-start-line="41" selection-start-column="15" selection-end-line="41" selection-end-column="15" />
-              <folding>
-                <element signature="e#6#905#0#PHP" expanded="true" />
-              </folding>
-            </state>
-          </provider>
-        </entry>
-      </file>
     </leaf>
   </component>
   <component name="FileTemplateManagerImpl">
@@ -104,6 +48,11 @@
   </component>
   <component name="Git.Settings">
     <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$" />
+    <option name="RECENT_BRANCH_BY_REPOSITORY">
+      <map>
+        <entry key="$PROJECT_DIR$" value="php54compatibility" />
+      </map>
+    </option>
   </component>
   <component name="IdeDocumentHistory">
     <option name="CHANGED_PATHS">
@@ -132,12 +81,13 @@
         <option value="$PROJECT_DIR$/php/helper.php" />
         <option value="$PROJECT_DIR$/php/download.php" />
         <option value="$PROJECT_DIR$/php/upload.php" />
-        <option value="$PROJECT_DIR$/php/module.calendar.php" />
         <option value="$PROJECT_DIR$/resources/css/calendarimporter-main.css" />
         <option value="$PROJECT_DIR$/js/plugin.calendarimporter.js" />
         <option value="$PROJECT_DIR$/js/ui/ContextMenu.js" />
         <option value="$PROJECT_DIR$/js/data/Actions.js" />
         <option value="$PROJECT_DIR$/js/dialogs/ImportPanel.js" />
+        <option value="$PROJECT_DIR$/php/composer.json" />
+        <option value="$PROJECT_DIR$/php/module.calendar.php" />
       </list>
     </option>
   </component>
@@ -152,10 +102,10 @@
   </component>
   <component name="PhpWorkspaceProjectConfiguration" backward_compatibility_performed="true" />
   <component name="ProjectFrameBounds">
-    <option name="x" value="145" />
-    <option name="y" value="602" />
-    <option name="width" value="1782" />
-    <option name="height" value="941" />
+    <option name="x" value="65" />
+    <option name="y" value="24" />
+    <option name="width" value="1776" />
+    <option name="height" value="983" />
   </component>
   <component name="ProjectLevelVcsManager" settingsEditedManually="false">
     <OptionsSetting value="true" id="Add" />
@@ -182,8 +132,6 @@
       <foldersAlwaysOnTop value="true" />
     </navigator>
     <panes>
-      <pane id="Scratches" />
-      <pane id="Scope" />
       <pane id="ProjectPane">
         <subPane>
           <PATH>
@@ -318,6 +266,8 @@
           </PATH>
         </subPane>
       </pane>
+      <pane id="Scope" />
+      <pane id="Scratches" />
     </panes>
   </component>
   <component name="PropertiesComponent">
@@ -389,17 +339,21 @@
       <workItem from="1477949603566" duration="9204000" />
       <workItem from="1480441197414" duration="11151000" />
       <workItem from="1480505014387" duration="3401000" />
+      <workItem from="1480509394154" duration="63000" />
+      <workItem from="1480548170124" duration="207000" />
+      <workItem from="1480584080034" duration="27000" />
+      <workItem from="1480955138355" duration="887000" />
     </task>
     <servers />
   </component>
   <component name="TimeTrackingManager">
-    <option name="totallyTimeSpent" value="23756000" />
+    <option name="totallyTimeSpent" value="24940000" />
   </component>
   <component name="ToolWindowManager">
-    <frame x="145" y="602" width="1782" height="941" extended-state="0" />
+    <frame x="65" y="24" width="1776" height="983" extended-state="6" />
     <editor active="true" />
     <layout>
-      <window_info id="Project" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="true" show_stripe_button="true" weight="0.2514029" sideWeight="0.5" order="0" side_tool="false" content_ui="combo" />
+      <window_info id="Project" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="true" show_stripe_button="true" weight="0.2528153" sideWeight="0.5" order="0" side_tool="false" content_ui="combo" />
       <window_info id="TODO" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="6" side_tool="false" content_ui="tabs" />
       <window_info id="Event Log" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="7" side_tool="true" content_ui="tabs" />
       <window_info id="Database" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="3" side_tool="false" content_ui="tabs" />
@@ -436,11 +390,45 @@
     <watches-manager />
   </component>
   <component name="editorHistoryManager">
+    <entry file="file://$PROJECT_DIR$/php/module.calendar.php">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="3465">
+          <caret line="231" column="30" selection-start-line="231" selection-start-column="25" selection-end-line="231" selection-end-column="30" />
+          <folding>
+            <element signature="e#6#914#0#PHP" expanded="true" />
+            <element signature="e#1004#1022#0#PHP" expanded="true" />
+          </folding>
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/js/data/Actions.js">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="2295">
+          <caret line="173" column="35" selection-start-line="173" selection-start-column="35" selection-end-line="173" selection-end-column="80" />
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/js/dialogs/ImportPanel.js">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="0">
+          <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/php/helper.php">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="615">
+          <caret line="41" column="15" selection-start-line="41" selection-start-column="15" selection-end-line="41" selection-end-column="15" />
+          <folding>
+            <element signature="e#6#905#0#PHP" expanded="true" />
+          </folding>
+        </state>
+      </provider>
+    </entry>
     <entry file="file://$PROJECT_DIR$/js/plugin.calendarimporter.js">
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="0">
           <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -448,7 +436,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="1440">
           <caret line="96" column="123" selection-start-line="96" selection-start-column="123" selection-end-line="96" selection-end-column="123" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -456,7 +443,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="675">
           <caret line="65" column="47" selection-start-line="65" selection-start-column="47" selection-end-line="65" selection-end-column="47" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -464,7 +450,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="1515">
           <caret line="101" column="30" selection-start-line="101" selection-start-column="30" selection-end-line="101" selection-end-column="30" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -472,7 +457,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="1275">
           <caret line="85" column="59" selection-start-line="85" selection-start-column="59" selection-end-line="85" selection-end-column="59" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -487,9 +471,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="60">
           <caret line="24" column="47" selection-start-line="24" selection-start-column="47" selection-end-line="24" selection-end-column="47" />
-          <folding>
-            <element signature="e#21#926#0#PHP" expanded="false" />
-          </folding>
         </state>
       </provider>
     </entry>
@@ -536,13 +517,6 @@
         </state>
       </provider>
     </entry>
-    <entry file="file://$PROJECT_DIR$/php/composer.json">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-        </state>
-      </provider>
-    </entry>
     <entry file="file://$PROJECT_DIR$/js/data/CalendarHelper.js" />
     <entry file="file://$PROJECT_DIR$/backend/functions.php">
       <provider selected="true" editor-type-id="text-editor">
@@ -562,9 +536,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="60">
           <caret line="24" column="47" selection-start-line="24" selection-start-column="47" selection-end-line="24" selection-end-column="47" />
-          <folding>
-            <element signature="e#21#926#0#PHP" expanded="false" />
-          </folding>
         </state>
       </provider>
     </entry>
@@ -587,12 +558,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="744">
           <caret line="61" column="71" selection-start-line="61" selection-start-column="71" selection-end-line="61" selection-end-column="71" />
-          <folding>
-            <marker date="1480442383471" expanded="true" signature="1214:1218" ph="&lt;" />
-            <marker date="1480442383471" expanded="true" signature="1244:1248" ph="&gt;" />
-            <marker date="1480442383471" expanded="true" signature="2881:2885" ph="&lt;" />
-            <marker date="1480442383471" expanded="true" signature="2905:2909" ph="&gt;" />
-          </folding>
         </state>
       </provider>
     </entry>
@@ -607,7 +572,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="435">
           <caret line="44" column="93" selection-start-line="44" selection-start-column="57" selection-end-line="44" selection-end-column="93" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -622,7 +586,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="0">
           <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="20" selection-end-column="3" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -644,7 +607,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="585">
           <caret line="147" column="28" selection-start-line="147" selection-start-column="28" selection-end-line="147" selection-end-column="64" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -659,7 +621,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="15">
           <caret line="1" column="29" selection-start-line="1" selection-start-column="29" selection-end-line="1" selection-end-column="29" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -698,7 +659,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="30">
           <caret line="2" column="59" selection-start-line="2" selection-start-column="54" selection-end-line="2" selection-end-column="59" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -721,7 +681,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="-165">
           <caret line="13" column="25" selection-start-line="13" selection-start-column="22" selection-end-line="13" selection-end-column="25" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -736,7 +695,6 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="1440">
           <caret line="96" column="123" selection-start-line="96" selection-start-column="123" selection-end-line="96" selection-end-column="123" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -744,15 +702,12 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="675">
           <caret line="45" column="12" selection-start-line="45" selection-start-column="12" selection-end-line="45" selection-end-column="50" />
-          <folding>
-            <element signature="e#6#907#0#PHP" expanded="true" />
-          </folding>
         </state>
       </provider>
     </entry>
     <entry file="file://$PROJECT_DIR$/php/helper.php">
       <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="407">
+        <state relative-caret-position="615">
           <caret line="41" column="15" selection-start-line="41" selection-start-column="15" selection-end-line="41" selection-end-column="15" />
           <folding>
             <element signature="e#6#905#0#PHP" expanded="true" />
@@ -762,38 +717,22 @@
     </entry>
     <entry file="file://$PROJECT_DIR$/php/upload.php">
       <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="408">
+        <state relative-caret-position="510">
           <caret line="34" column="0" selection-start-line="34" selection-start-column="0" selection-end-line="39" selection-end-column="1" />
-          <folding>
-            <element signature="e#6#905#0#PHP" expanded="true" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/php/module.calendar.php">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="260">
-          <caret line="231" column="30" selection-start-line="231" selection-start-column="25" selection-end-line="231" selection-end-column="30" />
-          <folding>
-            <element signature="e#6#914#0#PHP" expanded="true" />
-            <element signature="e#1004#1022#0#PHP" expanded="true" />
-          </folding>
         </state>
       </provider>
     </entry>
     <entry file="file://$PROJECT_DIR$/js/plugin.calendarimporter.js">
       <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="610">
+        <state relative-caret-position="1365">
           <caret line="91" column="27" selection-start-line="91" selection-start-column="27" selection-end-line="91" selection-end-column="27" />
-          <folding />
         </state>
       </provider>
     </entry>
     <entry file="file://$PROJECT_DIR$/js/data/Actions.js">
       <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="268">
+        <state relative-caret-position="2295">
           <caret line="173" column="35" selection-start-line="173" selection-start-column="35" selection-end-line="173" selection-end-column="80" />
-          <folding />
         </state>
       </provider>
     </entry>
@@ -801,8 +740,23 @@
       <provider selected="true" editor-type-id="text-editor">
         <state relative-caret-position="583">
           <caret line="113" column="29" selection-start-line="113" selection-start-column="21" selection-end-line="113" selection-end-column="29" />
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/php/composer.json">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="60">
+          <caret line="4" column="1" selection-start-line="4" selection-start-column="1" selection-end-line="4" selection-end-column="1" />
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/php/module.calendar.php">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="279">
+          <caret line="691" column="13" selection-start-line="691" selection-start-column="13" selection-end-line="691" selection-end-column="13" />
           <folding>
-            <element signature="n#!!doc" expanded="true" />
+            <element signature="e#6#914#0#PHP" expanded="true" />
+            <element signature="e#1004#1022#0#PHP" expanded="true" />
           </folding>
         </state>
       </provider>
diff --git a/php/module.calendar.php b/php/module.calendar.php
index 80da133..53e9b94 100644
--- a/php/module.calendar.php
+++ b/php/module.calendar.php
@@ -680,8 +680,16 @@ class CalendarModule extends Module
             if (!empty((string)$vEvent->{'X-ZARAFA-LABEL'})) {
                 $properties["label"] = array_search((string)$vEvent->{'X-ZARAFA-LABEL'}, $this->labels);
             }
-            $properties["last_modification_time"] = (string)$vEvent->{'LAST-MODIFIED'}->getDateTime()->getTimestamp();
-            $properties["creation_time"] = (string)$vEvent->CREATED->getDateTime()->getTimestamp();
+            if (!empty((string)$vEvent->{'LAST-MODIFIED'})) {
+                $properties["last_modification_time"] = (string)$vEvent->{'LAST-MODIFIED'}->getDateTime()->getTimestamp();
+            } else {
+                $properties["last_modification_time"] = time();
+            }
+            if (!empty((string)$vEvent->CREATED)) {
+                $properties["creation_time"] = (string)$vEvent->CREATED->getDateTime()->getTimestamp();
+            } else {
+                $properties["creation_time"] = time();
+            }
             $properties["rrule"] = (string)$vEvent->RRULE;
 
             // Attendees