Allow Set::extract() to match null.

Fixes #2926

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

@@ -1387,6 +1387,33 @@ class SetTest extends CakeTestCase {
 		$this->assertEquals($expected, $result);
 	}
 
+/**
+ * Test that extract() + matching can hit null things.
+ */
+	public function testExtractMatchesNull() {
+		$data = array(
+			'Country' => array(
+				array('name' => 'Canada'),
+				array('name' => 'Australia'),
+				array('name' => null),
+			)
+		);
+		$result = Set::extract('/Country[name=/Canada|^$/]', $data);
+		$expected = array(
+			array(
+				'Country' => array(
+					'name' => 'Canada',
+				),
+			),
+			array(
+				'Country' => array(
+					'name' => null,
+				),
+			),
+		);
+		$this->assertEquals($expected, $result);
+	}
+
 /**
  * testMatches method
  *

lib/Cake/Utility/Set.php

@@ -536,7 +536,7 @@ class Set {
 				continue;
 			}
 			list(, $key, $op, $expected) = $match;
-			if (!isset($data[$key])) {
+			if (!(isset($data[$key]) || array_key_exists($key, $data))) {
 				return false;
 			}