diff --git a/main/inc/lib/api.lib.php b/main/inc/lib/api.lib.php
index 8491a6a36f..1b59423c41 100644
--- a/main/inc/lib/api.lib.php
+++ b/main/inc/lib/api.lib.php
@@ -2635,7 +2635,7 @@ function api_is_coach($session_id = 0, $courseId = null, $check_student_view = t
     if (!empty($session_id)) {
         $sql = "SELECT DISTINCT id, name, access_start_date, access_end_date
                 FROM $session_table
-                WHERE session.id_coach =  '".$userId."' AND id = '$session_id'
+                WHERE session.id_coach = $userId AND id = $session_id
                 ORDER BY access_start_date, access_end_date, name";
         $result = Database::query($sql);
         if (!empty($sessionIsCoach)) {
@@ -3015,7 +3015,6 @@ function api_is_coach_of_course_in_session($sessionId)
     return false;
 }
 
-
 /**
 * Checks if a student can edit contents in a session depending
 * on the session visibility
@@ -3054,7 +3053,6 @@ function api_is_allowed_to_session_edit($tutor = false, $coach = false)
                 case SESSION_AVAILABLE:         //5
                     return true;
             }
-
         }
     }
 }
@@ -3348,7 +3346,7 @@ function api_not_allowed($print_headers = false, $message = null)
             $msg .= "<div style='display:none;'>";
         }
         $msg .= '<div class="well">';
-        $msg .= $form->return_form();
+        $msg .= $form->returnForm();
         $msg .='</div>';
         if ($casEnabled) {
             $msg .= "</div>";
@@ -3936,6 +3934,7 @@ function api_get_item_property_id($course_code, $tool, $ref, $sessionId = 0)
     // Definition of tables.
     $tableItemProperty = Database::get_course_table(TABLE_ITEM_PROPERTY);
     $course_id = $course_info['real_id'];
+    $sessionId = (int) $sessionId;
     $sessionCondition = " AND session_id = $sessionId ";
     if (empty($sessionId)) {
         $sessionCondition = " AND (session_id = 0 OR session_id IS NULL) ";
@@ -4072,7 +4071,6 @@ function api_get_item_property_info($course_id, $tool, $ref, $session_id = 0, $g
  * (in some cases, like the indexing language picker, it can alter the presentation)
  * @return string
  */
-
 function api_get_languages_combo($name = 'language')
 {
     $ret = '';
@@ -4433,23 +4431,6 @@ function api_max_sort_value($user_course_category, $user_id)
     return 0;
 }
 
-/**
- * This function converts the string "true" or "false" to a boolean true or false.
- * This function is in the first place written for the Chamilo Config Settings (also named AWACS)
- * @param string "true" or "false"
- * @return boolean true or false
- * @author Patrick Cool <patrick.cool@UGent.be>, Ghent University
- */
-function api_string_2_boolean($string) {
-    if ($string == 'true') {
-        return true;
-    }
-    if ($string == 'false') {
-        return false;
-    }
-    return false;
-}
-
 /**
  * Determines the number of plugins installed for a given location
  */
@@ -4895,9 +4876,9 @@ function parse_info_file($filename) {
  * Gets Chamilo version from the configuration files
  * @return string   A string of type "1.8.4", or an empty string if the version could not be found
  */
-function api_get_version() {
-    global $_configuration;
-    return (string)$_configuration['system_version'];
+function api_get_version()
+{
+    return (string) api_get_configuration_value('system_version');
 }
 
 /**
@@ -8078,7 +8059,7 @@ function api_is_date_in_date_range($startDate, $endDate, $currentDate = null)
     $endDate = strtotime(api_get_local_time($endDate));
     $currentDate = strtotime(api_get_local_time($currentDate));
 
-    if (($currentDate >= $startDate) && ($currentDate <= $endDate)) {
+    if ($currentDate >= $startDate && $currentDate <= $endDate) {
         return true;
     }
 
@@ -8175,4 +8156,3 @@ function api_remove_uploaded_file($type, $file)
         unlink($path);
     }
 }
-
diff --git a/main/inc/lib/usermanager.lib.php b/main/inc/lib/usermanager.lib.php
index 4673c50706..de53328bcb 100755
--- a/main/inc/lib/usermanager.lib.php
+++ b/main/inc/lib/usermanager.lib.php
@@ -2776,7 +2776,7 @@ class UserManager
 
                 // This query is horribly slow when more than a few thousand
                 // users and just a few sessions to which they are subscribed
-                $personal_course_list_sql = "SELECT DISTINCT
+                $sql = "SELECT DISTINCT
                         course.code code,
                         course.title i,
                         ".(api_is_western_name_order() ? "CONCAT(user.firstname,' ',user.lastname)" : "CONCAT(user.lastname,' ',user.firstname)")." t,
@@ -2800,8 +2800,7 @@ class UserManager
                             OR session.id_coach = $user_id
                         )
                     ORDER BY i";
-                $course_list_sql_result = Database::query($personal_course_list_sql);
-
+                $course_list_sql_result = Database::query($sql);
                 while ($result_row = Database::fetch_array($course_list_sql_result, 'ASSOC')) {
                     $result_row['course_info'] = api_get_course_info($result_row['code']);
                     $key = $result_row['session_id'].' - '.$result_row['code'];
@@ -2819,7 +2818,7 @@ class UserManager
 
             /* This query is very similar to the above query,
                but it will check the session_rel_course_user table if there are courses registered to our user or not */
-            $personal_course_list_sql = "SELECT DISTINCT
+            $sql = "SELECT DISTINCT
                 course.code code,
                 course.title i, CONCAT(user.lastname,' ',user.firstname) t,
                 email,
@@ -2840,8 +2839,7 @@ class UserManager
             WHERE session_course_user.user_id = $user_id
             ORDER BY i";
 
-            $course_list_sql_result = Database::query($personal_course_list_sql);
-
+            $course_list_sql_result = Database::query($sql);
             while ($result_row = Database::fetch_array($course_list_sql_result, 'ASSOC')) {
                 $result_row['course_info'] = api_get_course_info($result_row['code']);
                 $key = $result_row['session_id'].' - '.$result_row['code'];
@@ -3036,15 +3034,18 @@ class UserManager
                     $return = "<h4>$course</h4>";
                     $return .= '<ul class="thumbnails">';
                 }
+                $extensionList = ['jpg', 'jpeg', 'png', 'gif', 'bmp', 'tif'];
                 foreach ($file_list as $file) {
                     if ($resourcetype == "all") {
                         $return .= '<li><a href="'.$web_path.urlencode($file).'" target="_blank">'.htmlentities($file).'</a></li>';
                     } elseif ($resourcetype == "images") {
                         //get extension
                         $ext = explode('.', $file);
-                        if ($ext[1] == 'jpg' || $ext[1] == 'jpeg' || $ext[1] == 'png' || $ext[1] == 'gif' || $ext[1] == 'bmp' || $ext[1] == 'tif') {
-                            $return .= '<li class="span2"><a class="thumbnail" href="'.$web_path.urlencode($file).'" target="_blank">
-                                            <img src="'.$web_path.urlencode($file).'" ></a>
+                        if (isset($ext[1]) && in_array($ext[1], $extensionList)) {
+                            $return .= '<li class="span2">
+                                            <a class="thumbnail" href="'.$web_path.urlencode($file).'" target="_blank">
+                                                <img src="'.$web_path.urlencode($file).'" >
+                                            </a>
                                         </li>';
                         }
                     }
diff --git a/tests/main/inc/lib/main_api.lib.test.php b/tests/main/inc/lib/main_api.lib.test.php
index 51a3c392ce..08d8f33c3c 100755
--- a/tests/main/inc/lib/main_api.lib.test.php
+++ b/tests/main/inc/lib/main_api.lib.test.php
@@ -454,12 +454,6 @@ class TestMainApi extends UnitTestCase {
 		//var_dump($res);
 	}
 
-	function testString2Boolean(){
-		global $string;
-		$res=api_string_2_boolean($string);
-		$this->assertFalse($res);
-	}
-
 	function testApiNumberOfPlugins(){
 		global $_plugins;
 		$location=2;