Fix model field defaults to an empty string and is determined to be null

CHANGELOG.md

@@ -1,4 +1,5 @@
 # [3.0.4](https://github.com/phalcon/cphalcon/releases/tag/v3.0.4) (XXXX-XX-XX)
+- Fixed Isnull check is not correct when the model field defaults to an empty string. [#12507](https://github.com/phalcon/cphalcon/issues/12507)
 
 # [3.0.3](https://github.com/phalcon/cphalcon/releases/tag/v3.0.3) (2016-12-24)
 - Fixed implementation of Iterator interface in a `Phalcon\Forms\Form` that could cause a run-time warning

phalcon/mvc/model.zep

@@ -2045,8 +2045,8 @@ abstract class Model implements EntityInterface, ModelInterface, ResultInterface
 					let automaticAttributes = metaData->getAutomaticUpdateAttributes(this);
 				} else {
 					let automaticAttributes = metaData->getAutomaticCreateAttributes(this);
-					let defaultValues = metaData->getDefaultValues(this);
 				}
+                let defaultValues = metaData->getDefaultValues(this);
 
 				/**
 				 * Get string attributes that allow empty strings as defaults
@@ -2088,7 +2088,7 @@ abstract class Model implements EntityInterface, ModelInterface, ResultInterface
 											let isNull = true;
 										}
 									} else {
-										if value === null || value === "" {
+										if value === null || (value === "" && value !== defaultValues[field]) {
 											let isNull = true;
 										}
 									}

tests/unit/Mvc/ModelTest.php

@@ -2,6 +2,7 @@
 
 namespace Phalcon\Test\Unit\Mvc;
 
+use Phalcon\Test\Models\Personers;
 use Phalcon\Test\Models\Users;
 use Phalcon\Cache\Backend\Apc;
 use Phalcon\Test\Models\Robots;
@@ -754,4 +755,38 @@ function () {
             }
         );
     }
+
+    /**
+     * for PR #12507
+     */
+    public function testFieldDefaultEmptyStringIsNull()
+    {
+        $this->specify(
+            'The field default value is empty string and is determined to be null',
+            function () {
+                $personers               = new Personers();
+                $personers->borgerId     = 'id-' . time() . rand(1, 99);
+                $personers->slagBorgerId = 1;
+                $personers->kredit       = 2.3;
+                $personers->status       = 'A';
+
+                //  test field for create
+                $personers->navnes = '';
+                $created           = $personers->create();
+                expect($created)->true();
+
+                //  write something to not null default '' field
+                $personers->navnes = 'save something!';
+                $saved             = $personers->save();
+                expect($saved)->true();
+
+                //  test field for update
+                $personers->navnes = '';
+                $saved             = $personers->save();
+                expect($saved)->true();
+
+                $personers->delete();
+            }
+        );
+    }
 }