Use stdClass when a microformat has no properties

Fixes microformats#171. Test based on the issue included.

Author: Zegnat

Mf2/Parser.php

@@ -1122,6 +1122,11 @@ public function parseH(\DOMElement $e, $is_backcompat = false, $has_nested_mf =
 		// Make sure things are unique and in alphabetical order
 		$mfTypes = array_unique($mfTypes);
 		sort($mfTypes);
+		
+		// Properties should be an object when JSON serialised
+		if (empty($return) and $this->jsonMode) {
+			$return = new stdClass();
+		}
 
 		// Phew. Return the final result.
 		$parsed = array(

tests/Mf2/CombinedMicroformatsTest.php

@@ -417,5 +417,17 @@ public function testMf2DoesNotParseRelTag() {
 		$this->assertArrayNotHasKey('category', $output['items'][1]['properties']);
 	}
 
+	/**
+	 * JSON-mode should return an empty stdClass when a microformat has no properties.
+	 * @see https://github.com/indieweb/php-mf2/issues/171
+	 */
+	public function testEmptyPropertiesObjectInJSONMode() {
+		$input = '<div class="h-feed"><div class="h-entry"></div></div>';
+		$parser = new Parser($input, null, true);
+		$output = $parser->parse();
+		$this->assertInstanceOf(\stdClass::class, $output['items'][0]['properties']);
+		$this->assertSame('{}', json_encode($output['items'][0]['properties']));
+	}
+
 }