FIX Type checking in objectForKey() to fix postgres bug

src/Forms/TreeDropdownField.php

@@ -812,10 +812,13 @@ protected function getSearchResults()
      * Get the object where the $keyField is equal to a certain value
      *
      * @param string|int $key
-     * @return DataObject
+     * @return DataObject|null
      */
     protected function objectForKey($key)
     {
+        if (!is_string($key) && !is_int($key)) {
+            return null;
+        }
         return DataObject::get($this->getSourceObject())
             ->filter($this->getKeyField(), $key)
             ->first();

tests/php/Forms/TreeDropdownFieldTest.php

@@ -8,7 +8,10 @@
 use SilverStripe\Dev\CSSContentParser;
 use SilverStripe\Dev\SapphireTest;
 use SilverStripe\Control\HTTPRequest;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\Form;
 use SilverStripe\Forms\TreeDropdownField;
+use SilverStripe\ORM\DataObject;
 use SilverStripe\ORM\Tests\HierarchyTest\TestObject;
 
 class TreeDropdownFieldTest extends SapphireTest
@@ -246,4 +249,21 @@ public function testReadonly()
             $result
         );
     }
+
+    /**
+     * This is to test setting $key to an Object in the protected function objectForKey()
+     * This is to fix an issue where postgres will not fail gracefully when you do this
+     */
+    public function testObjectForKeyObjectValue()
+    {
+        $form = Form::create();
+        $fieldList = FieldList::create();
+        $field = TreeDropdownField::create('TestTree', 'Test tree', File::class);
+        $fieldList->add($field);
+        $form->setFields($fieldList);
+        $field->setValue(DataObject::create());
+        // The following previously errored in postgres
+        $field->getSchemaStateDefaults();
+        $this->assertTrue(true);
+    }
 }