Merge pull request #235 from remicollet/issue-74

fix Trying to access array offset on value of type null (7.4)

Author: michalbundyra

src/Form.php

@@ -364,7 +364,12 @@ public function bindValues(array $values = [], array $validationGroup = null)
             $data = array_key_exists($this->baseFieldset->getName(), $data)
                 ? $data[$this->baseFieldset->getName()]
                 : [];
-            $this->object = $this->baseFieldset->bindValues($data, $validationGroup[$this->baseFieldset->getName()]);
+            $this->object = $this->baseFieldset->bindValues(
+                $data,
+                isset($validationGroup[$this->baseFieldset->getName()])
+                    ? $validationGroup[$this->baseFieldset->getName()]
+                    : []
+            );
         } else {
             $this->object = parent::bindValues($data, $validationGroup);
         }