Fix notice error when reading empty values.

When reading empty values a notice error would be triggered.
Slicing the first char off and comparing that solves this.

Fixes #2537

lib/Cake/Controller/Component/CookieComponent.php

@@ -483,7 +483,8 @@ protected function _implode(array $array) {
  * @return array Map of key and values
  */
 	protected function _explode($string) {
-		if ($string[0] === '{' || $string[0] === '[') {
+		$first = substr($string, 0, 1);
+		if ($first !== false && $first === '{' || $first === '[') {
 			$ret = json_decode($string, true);
 			return ($ret != null) ? $ret : $string;
 		}

lib/Cake/Test/Case/Controller/Component/CookieComponentTest.php

@@ -471,6 +471,21 @@ public function testReadLegacyCookieValue() {
 		$this->assertEquals($expected, $result);
 	}
 
+/**
+ * Test reading empty values.
+ */
+	public function testReadEmpty() {
+		$_COOKIE['CakeTestCookie'] = array(
+		  'JSON' => '{"name":"value"}',
+		  'Empty' => '',
+		  'String' => '{"somewhat:"broken"}'
+		);
+		$this->assertEqual(array('name' => 'value'), $this->Cookie->read('JSON'));
+		$this->assertEqual('value', $this->Cookie->read('JSON.name'));
+		$this->assertEqual('', $this->Cookie->read('Empty'));
+		$this->assertEqual('{"somewhat:"broken"}', $this->Cookie->read('String'));
+	}
+
 /**
  * test that no error is issued for non array data.
  *
@@ -483,6 +498,7 @@ public function testNoErrorOnNonArrayData() {
 		$this->assertNull($this->Cookie->read('value'));
 	}
 
+
 /**
  * test that deleting a top level keys kills the child elements too.
  *