diff --git a/src/includes/class/class.LSformElement_jsonCompositeAttribute.php b/src/includes/class/class.LSformElement_jsonCompositeAttribute.php
index 523413f9..71d40ace 100644
--- a/src/includes/class/class.LSformElement_jsonCompositeAttribute.php
+++ b/src/includes/class/class.LSformElement_jsonCompositeAttribute.php
@@ -242,18 +242,24 @@ class LSformElement_jsonCompositeAttribute extends LSformElement {
 
     // Extract value form POST data
     $parseValues = array();
+    $present = false;
     // API mode
     if ($this -> form -> api_mode) {
+      $present = isset($_POST[$this -> name]);
       $json_values = $this -> getData($_POST, $this -> name);
-      if (!is_array($json_values) || empty($json_values)) {
-        self :: log_trace($this." -> getPostData(): not in POST data");
-        return true;
-      }
+      self :: log_trace(
+        $this." -> getPostData(onlyIfPresent=".($onlyIfPresent?1:0)."): ".
+        "raw JSON values = ".varDump($json_values)
+      );
 
       $json_value_count = 0;
-      foreach($json_values as $json_value) {
+      foreach((is_array($json_values)?$json_values:array()) as $json_value) {
         $json_value_count += 1;
         $input_value = json_decode($json_value, true);
+        self :: log_trace(
+          $this." -> getPostData(onlyIfPresent=".($onlyIfPresent?1:0)."): ".
+          "raw JSON value #$json_value_count = ".varDump($input_value)
+        );
         if (!is_array($input_value)) {
           $this -> form -> setElementError(
             $this -> attr_html,
@@ -290,13 +296,19 @@ class LSformElement_jsonCompositeAttribute extends LSformElement {
         }
 
         // Ignore empty value from form
-        if (empty($unemptyComponents))
+        if (empty($unemptyComponents)) {
+          $this -> form -> setElementError(
+            $this -> attr_html,
+            getFData(_('JSON value #%{idx} is invalid (or empty).'), $json_value_count)
+          );
           continue;
+        }
 
         $parseValues[] = $parseValue;
       }
     }
     elseif (is_array($_POST[$this -> name.'__values_uuid'])) {
+      $present = true;
       // HTML form mode
       foreach ($_POST[$this -> name.'__values_uuid'] as $uuid) {
         $parseValue = array();
@@ -330,6 +342,7 @@ class LSformElement_jsonCompositeAttribute extends LSformElement {
       }
     }
 
+    $return[$this -> name] = array();
     // Check extracted values
     foreach ($parseValues as $parseValue) {
       // Check component value
@@ -351,6 +364,14 @@ class LSformElement_jsonCompositeAttribute extends LSformElement {
       $return[$this -> name][] = json_encode($parseValue);
     }
 
+    if (!$present && $onlyIfPresent) {
+      self :: log_trace(
+        $this." -> getPostData(onlyIfPresent=".($onlyIfPresent?1:0)."): ".
+        "not present in POST data, ignore it."
+      );
+      unset($return[$this -> name]);
+    }
+
     return true;
   }