CSSStyleDeclaraction returns empty string

LayoutTests/imported/csswg-test/css-shapes-1/shape-outside/values/support/parsing-utils.js

 var ParsingUtils = (function() {
 function testInlineStyle(value, expected) {
     var div = document.createElement('div');
     div.style.setProperty('shape-outside', value);
     var actual = div.style.getPropertyValue('shape-outside');
     assert_equals(actual, expected);
 }
 
 function testComputedStyle(value, expected) {
     var div = document.createElement('div');
@@ skipping 80 matching lines @@
         assert_equals(actual, !expected ? '0' : expected);
     }
 }
 
 // Builds an array of test cases to send to testharness.js where one test case is: [name, actual, expected]
 // These test cases will verify results from testInlineStyle() or testComputedStyle()
 function buildTestCases(testCases, testType) {
     var results = [];
 
     // If test_type isn't specified, test inline style
-    var type = typeof testType == 'undefined' ? 'invalid': testType;
+    var type = typeof testType == 'undefined' ? 'empty_string': testType;
 
     testCases.forEach(function(test) {
         oneTestCase = [];
 
-        // name - annotated by type (inline vs. computed)
+        // name - annotated by type (empty_string vs. computed)
         if ( test.hasOwnProperty('name') ) {
             oneTestCase.push(test['name'] +' - '+ type);
         } else {
             // If test_name isn't specified, use the actual
             oneTestCase.push(test['actual'] +' - '+ type);
         }
 
         // actual
         oneTestCase.push(test['actual'])
 
         // expected
-        if( type.indexOf('invalid') != -1 ){
-            oneTestCase.push(null)
+        if( type.indexOf('empty_string') != -1 ){
+            oneTestCase.push('')
         } else if( type == 'inline' ) {
             oneTestCase.push(test['expected_inline']);
         } else if( type == 'computed' ){
             oneTestCase.push( convertToPx(test['expected_computed']) );
         }
         results.push(oneTestCase);
     });
     return results;
 }
 
@@ skipping 37 matching lines @@
                     testCase.push(expected);
                     results.push(testCase);
                 }
             });
         } else {
             invalidPositions.forEach(function(test) {
                 var testValue = shape + '(at ' + setUnit(test, false, units) +')';
                 testCase = new Array();
                 testCase.push(testValue + ' is invalid');
                 testCase.push(testValue);
-                testCase.push(null);
+                testCase.push("");
                 results.push(testCase);
             });
         }
     }
     return unique(results);
 }
 
 function buildRadiiTests(shape, type, units) {
     var results = new Array();
     var testUnits = typeof units == 'undefined' ? 'px': units;
@@ skipping 669 matching lines @@
     buildPositionTests: buildPositionTests,
     buildInsetTests: buildInsetTests,
     buildPolygonTests: buildPolygonTests,
     generateInsetRoundCases: generateInsetRoundCases,
     buildCalcTests: buildCalcTests,
     validUnits: validUnits,
     calcTestValues: calcTestValues,
     roundResultStr: roundResultStr
 }
 })();