[Form] Set a child type to text if added to the form without a type.

This copies the behaviour of the FormBuilder::create() to the Form::add().

src/Symfony/Component/Form/Form.php

@@ -873,6 +873,10 @@ class Form implements \IteratorAggregate, FormInterface
             // Never initialize child forms automatically
             $options['auto_initialize'] = false;
 
+            if (null === $type && null === $this->config->getDataClass()) {
+                $type = 'text';
+            }
+
             if (null === $type) {
                 $child = $this->config->getFormFactory()->createForProperty($this->config->getDataClass(), $child, null, $options);
             } else {

src/Symfony/Component/Form/Tests/CompoundFormTest.php

@@ -207,6 +207,22 @@ class CompoundFormTest extends AbstractFormTest
         $this->assertSame(array(0 => $child), $this->form->all());
     }
 
+    public function testAddWithoutType()
+    {
+        $child = $this->getBuilder('foo')->getForm();
+
+        $this->factory->expects($this->once())
+            ->method('createNamed')
+            ->with('foo', 'text')
+            ->will($this->returnValue($child));
+
+        $this->form->add('foo');
+
+        $this->assertTrue($this->form->has('foo'));
+        $this->assertSame($this->form, $child->getParent());
+        $this->assertSame(array('foo' => $child), $this->form->all());
+    }
+
     public function testAddUsingNameButNoType()
     {
         $this->form = $this->getBuilder('name', null, '\stdClass')