Fix collection hydration problem

Author: svycka

src/Fieldset.php

@@ -11,6 +11,7 @@
 
 use Traversable;
 use Zend\Code\Reflection\ClassReflection;
+use Zend\Form\Element\Collection;
 use Zend\Hydrator;
 use Zend\Hydrator\HydratorAwareInterface;
 use Zend\Hydrator\HydratorInterface;
@@ -564,12 +565,18 @@ public function bindValues(array $values = [])
         $hydrator = $this->getHydrator();
         $hydratableData = [];
 
-        foreach ($values as $name => $value) {
-            if (!$this->has($name)) {
-                continue;
+        foreach ($this->iterator as $element) {
+            $name = $element->getName();
+
+            if (!array_key_exists($name, $values)) {
+                if (!($element instanceof Collection)) {
+                    continue;
+                }
+
+                $values[$name] = [];
             }
 
-            $element = $this->iterator->get($name);
+            $value = $values[$name];
 
             if ($element instanceof FieldsetInterface && $element->allowValueBinding()) {
                 $value = $element->bindValues($value);

test/FormTest.php

@@ -2135,4 +2135,39 @@ public function testSetValidationGroupOnFormWithNestedCollectionsPopulatesOnlyFi
 
         $this->assertEquals($data, $this->form->getData());
     }
+
+    public function testShouldHydrateEmptyCollection()
+    {
+        $fieldset = new Fieldset('example');
+        $fieldset->add([
+            'type' => 'Zend\Form\Element\Collection',
+            'name' => 'foo',
+            'options' => [
+                'label' => 'InputFilterProviderFieldset',
+                'count' => 1,
+                'target_element' => [
+                    'type' => 'text'
+                ]
+            ],
+        ]);
+
+        $this->form->add($fieldset);
+        $this->form->setBaseFieldset($fieldset);
+        $this->form->setHydrator(new \Zend\Hydrator\ObjectProperty());
+
+        $object = new Entity\SimplePublicProperty();
+        $object->foo = ['item 1', 'item 2'];
+
+        $this->form->bind($object);
+
+        $this->form->setData([
+            'submit' => 'Confirm',
+            'example' => [
+                //'foo' => [] // $_POST does't have this if collection is empty
+            ]
+        ]);
+
+        $this->assertTrue($this->form->isValid());
+        $this->assertEquals([], $this->form->getObject()->foo);
+    }
 }