Throw exceptions from Hash::combine()

When the key + value counts do not match Hash should throw an exception.
Silently doing the wrong thing is generally not a good idea. While this
change could break existing applications, those applications were
probably behaving incorrectly anyways.

Fixes #2470

lib/Cake/Test/Case/Utility/HashTest.php

@@ -1473,6 +1473,34 @@ public function testCombine() {
 		$this->assertEquals($expected, $result);
 	}
 
+/**
+ * test combine() giving errors on key/value length mismatches.
+ *
+ * @expectedException CakeException
+ * @return void
+ */
+	public function testCombineErrorMissingValue() {
+		$data = array(
+			array('User' => array('id' => 1, 'name' => 'mark')),
+			array('User' => array('name' => 'jose')),
+		);
+		Hash::combine($data, '{n}.User.id', '{n}.User.name');
+	}
+
+/**
+ * test combine() giving errors on key/value length mismatches.
+ *
+ * @expectedException CakeException
+ * @return void
+ */
+	public function testCombineErrorMissingKey() {
+		$data = array(
+			array('User' => array('id' => 1, 'name' => 'mark')),
+			array('User' => array('id' => 2)),
+		);
+		Hash::combine($data, '{n}.User.id', '{n}.User.name');
+	}
+
 /**
  * test combine() with a group path.
  *

lib/Cake/Utility/Hash.php

@@ -346,10 +346,15 @@ public static function combine(array $data, $keyPath, $valuePath = null, $groupP
 		} elseif (!empty($valuePath)) {
 			$vals = self::extract($data, $valuePath);
 		}
+		if (empty($vals)) {
+			$vals = array_fill(0, count($keys), null);
+		}
 
-		$count = count($keys);
-		for ($i = 0; $i < $count; $i++) {
-			$vals[$i] = isset($vals[$i]) ? $vals[$i] : null;
+		if (count($keys) !== count($vals)) {
+			throw new CakeException(__d(
+				'cake_dev',
+				'Hash::combine() needs an equal number of keys + values.'
+			));
 		}
 
 		if ($groupPath !== null) {