Fix string '0' not being exported correctly.

Fixes #3518

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

@@ -408,6 +408,32 @@ TEXT;
 		$this->assertTextEquals($expected, $result);
 	}
 
+/**
+ * Test exporting various kinds of false.
+ *
+ * @return void
+ */
+	public function testExportVarZero() {
+		$data = array(
+			'nothing' => '',
+			'null' => null,
+			'false' => false,
+			'szero' => '0',
+			'zero' => 0
+		);;
+		$result = Debugger::exportVar($data);
+		$expected = <<<TEXT
+array(
+	'nothing' => '',
+	'null' => null,
+	'false' => false,
+	'szero' => '0',
+	'zero' => (int) 0
+)
+TEXT;
+		$this->assertTextEquals($expected, $result);
+	}
+
 /**
  * testLog method
  *

lib/Cake/Utility/Debugger.php

@@ -489,7 +489,7 @@ class Debugger {
 			case 'float':
 				return '(float) ' . $var;
 			case 'string':
-				if (!trim($var)) {
+				if (trim($var) === '') {
 					return "''";
 				}
 				return "'" . $var . "'";