fix type error

Image.php

@@ -84,7 +84,8 @@ abstract class Image extends File
 	 */
     public function getVariant($size, $force_create = false, $important_create = null)
     {
-        if ($force_create && $important_create === null && is_array($this->variants) && array_key_exists($size, $this->variants) && $this->variants[$size]['size'] === null) {
+        if ($force_create && $important_create === null && is_array($this->variants) && array_key_exists($size, $this->variants) && is_array($this->variants[$size])
+            && $this->variants[$size]['size'] === null) {
             $important_create = true;
         }