Minor - Fix PHP warning when label is an array.

main/inc/lib/formvalidator/Element/DateTimePicker.php

@@ -36,6 +36,13 @@ class DateTimePicker extends HTML_QuickForm_text
             $value = api_format_date($value, DATE_TIME_FORMAT_LONG_24H);
         }
 
+        $label = $this->getLabel();
+        if (is_array($label) && isset($label[0])) {
+            $label = $label[0];
+        }
+
+        $resetFieldX = sprintf(get_lang('ResetFieldX'), $label);
+
         return '
             <div class="input-group">
                 <span class="input-group-addon cursor-pointer">
@@ -45,9 +52,9 @@ class DateTimePicker extends HTML_QuickForm_text
                 <input class="form-control" type="hidden" id="'.$id.'_alt" value="'.$value.'">
                 <span class="input-group-btn">
                     <button class="btn btn-default" type="button"
-                            title="'.sprintf(get_lang('ResetFieldX'), $this->_label).'">
+                            title="'.$resetFieldX.'">
                         <span class="fa fa-trash text-danger" aria-hidden="true"></span>
-                        <span class="sr-only">'.sprintf(get_lang('ResetFieldX'), $this->_label).'</span>
+                        <span class="sr-only">'.$resetFieldX.'</span>
                     </button>
                 </span>
             </div>