diff --git a/htdocs/comm/action/class/actioncomm.class.php b/htdocs/comm/action/class/actioncomm.class.php
index e8b0a9c3fe8..af988c0dfa6 100644
--- a/htdocs/comm/action/class/actioncomm.class.php
+++ b/htdocs/comm/action/class/actioncomm.class.php
@@ -1586,7 +1586,8 @@ class ActionComm extends CommonObject
 	 */
 	public function getTooltipContentArray($params)
 	{
-		global $langs;
+		global $langs, $form;
+
 		$langs->load('agenda');
 
 		$datas = array();
@@ -1646,8 +1647,14 @@ class ActionComm extends CommonObject
 		// show categories for this record only in ajax to not overload lists
 		if (isModEnabled('category') && !$nofetch) {
 			require_once DOL_DOCUMENT_ROOT . '/categories/class/categorie.class.php';
-			$form = new Form($this->db);
-			$datas['categories'] = '<br>' . $form->showCategories($this->id, Categorie::TYPE_ACTIONCOMM, 1);
+			if (empty($form)) {
+				include_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
+				$form = new Form($this->db);
+			}
+			$tmpcategstring = $form->showCategories($this->id, Categorie::TYPE_ACTIONCOMM, 1);
+			if ($tmpcategstring) {
+				$datas['categories'] = '<br>'.$tmpcategstring;
+			}
 		}
 
 		return $datas;
diff --git a/htdocs/core/class/html.form.class.php b/htdocs/core/class/html.form.class.php
index f32c0f4119f..3b3816446e9 100644
--- a/htdocs/core/class/html.form.class.php
+++ b/htdocs/core/class/html.form.class.php
@@ -9265,7 +9265,11 @@ class Form
 					$toprint[] = '<li class="select2-search-choice-dolibarr noborderoncategories"' . ($c->color ? ' style="background: #' . $c->color . ';"' : ' style="background: #bbb"') . '>' . $way . '</li>';
 				}
 			}
-			return '<div class="select2-container-multi-dolibarr"><ul class="select2-choices-dolibarr">' . implode(' ', $toprint) . '</ul></div>';
+			if (empty($toprint)) {
+				return '';
+			} else {
+				return '<div class="select2-container-multi-dolibarr"><ul class="select2-choices-dolibarr">' . implode(' ', $toprint) . '</ul></div>';
+			}
 		}
 
 		if ($rendermode == 0) {