Prevent sql error for uuids if id is specified as null

if the primary key is present in the data to be saved as null - prevent
passing the same key (id) twice and therefore triggering an sql error.

Signed-off-by: Mark Story <mark@mark-story.com>

cake/libs/model/model.php

@@ -1273,7 +1273,12 @@ function save($data = null, $validate = true, $fieldList = array()) {
 							($fInfo['type'] === 'string' || $fInfo['type'] === 'binary')
 						);
 						if (empty($this->data[$this->alias][$this->primaryKey]) && $isUUID) {
-							list($fields[], $values[]) = array($this->primaryKey, String::uuid());
+							if (array_key_exists($this->primaryKey, $this->data[$this->alias])) {
+								$j = array_search($this->primaryKey, $fields);
+								$values[$j] = String::uuid();
+							} else {
+								list($fields[], $values[]) = array($this->primaryKey, String::uuid());
+							}
 						}
 						break;
 					}

cake/tests/cases/libs/model/model_write.test.php

@@ -161,6 +161,29 @@ function testAutoSaveUuid() {
 		);
 		$this->assertEqual(strlen($result['Uuid']['id']), 36);
 	}
+/**
+ * Ensure that if the id key is null but present the save doesn't fail (with an
+ * x sql error: "Column id specified twice")
+ *
+ * @return void
+ * @access public
+ */
+	function testSaveUuidNull() {
+		// SQLite does not support non-integer primary keys
+		$this->skipIf($this->db->config['driver'] == 'sqlite');
+
+		$this->loadFixtures('Uuid');
+		$TestModel =& new Uuid();
+
+		$TestModel->save(array('title' => 'Test record', 'id' => null));
+		$result = $TestModel->findByTitle('Test record');
+		$this->assertEqual(
+			array_keys($result['Uuid']),
+			array('id', 'title', 'count', 'created', 'updated')
+		);
+		$this->assertEqual(strlen($result['Uuid']['id']), 36);
+	}
+
 /**
  * testZeroDefaultFieldValue method
  *