[Form] Fix return types in form builder

Author: Tobion

ButtonBuilder.php

@@ -430,10 +430,12 @@ public function setIsEmptyCallback(?callable $isEmptyCallback)
 
     /**
      * Unsupported method.
+     *
+     * @throws BadMethodCallException
      */
     public function getEventDispatcher()
     {
-        return null;
+        throw new BadMethodCallException('Buttons do not support event dispatching.');
     }
 
     /**
@@ -626,26 +628,32 @@ public function getFormFactory()
 
     /**
      * Unsupported method.
+     *
+     * @throws BadMethodCallException
      */
     public function getAction()
     {
-        return null;
+        throw new BadMethodCallException('Buttons do not support actions.');
     }
 
     /**
      * Unsupported method.
+     *
+     * @throws BadMethodCallException
      */
     public function getMethod()
     {
-        return null;
+        throw new BadMethodCallException('Buttons do not support methods.');
     }
 
     /**
      * Unsupported method.
+     *
+     * @throws BadMethodCallException
      */
     public function getRequestHandler()
     {
-        return null;
+        throw new BadMethodCallException('Buttons do not support request handlers.');
     }
 
     /**

FormConfigBuilder.php

@@ -88,11 +88,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      */
     private $formFactory;
 
-    /**
-     * @var string|null
-     */
-    private $action;
-
+    private $action = '';
     private $method = 'POST';
 
     /**
@@ -396,6 +392,10 @@ public function getDataLocked()
      */
     public function getFormFactory()
     {
+        if (!isset($this->formFactory)) {
+            throw new BadMethodCallException('The form factory must be set before retrieving it.');
+        }
+
         return $this->formFactory;
     }