fix: pr review changes

Author: HardeepAsrani

classes/Visualizer/Module.php

@@ -277,7 +277,7 @@ private function _getCSV( $rows, $filename, $enclose ) {
 			$fp = fopen( wp_tempnam(), 'w+' );
 		}
 		if ( ! $fp ) {
-			return array( 'csv' => '', 'name' => $filename, 'string' => '' );
+			return null;
 		}
 		if ( ! apply_filters( 'vizualizer_export_include_series_type', true ) ) {
 			unset( $rows[1] );

tests/test-export.php

@@ -64,7 +64,7 @@ private function create_chart() {
 	 * @since 3.11.0
 	 *
 	 * @access private
-	 * @return object
+	 * @return object|null
 	 */
 	private function run_export() {
 		$_GET = array(
@@ -115,6 +115,9 @@ public function test_csv_export_response_structure() {
 		$this->_setRole( 'administrator' );
 
 		$response = $this->run_export();
+		$this->assertIsObject( $response );
+		$this->assertTrue( property_exists( $response, 'success' ) );
+		$this->assertTrue( property_exists( $response, 'data' ) );
 		$this->assertTrue( $response->success );
 
 		$data = $response->data;