var_export dumps null as NULL

correct for that so code standards are met with the results

lib/Cake/Console/Command/Task/FixtureTask.php

@@ -362,6 +362,9 @@ class FixtureTask extends BakeTask {
 			$values = array();
 			foreach ($record as $field => $value) {
 				$val = var_export($value, true);
+				if ($val === 'NULL') {
+					$val = 'null';
+				}
 				$values[] = "\t\t\t'$field' => $val";
 			}
 			$out .= "\t\tarray(\n";