CSSStyleDeclaraction returns empty string

LayoutTests/fast/css/script-tests/background-clip-text.js

Index: LayoutTests/fast/css/script-tests/background-clip-text.js
diff --git a/LayoutTests/fast/css/script-tests/background-clip-text.js b/LayoutTests/fast/css/script-tests/background-clip-text.js
index 98c958f10f89c16467bd57de4c25202518fd754e..76a6ceebb90405abd18a228eda607702be50d54c 100644
--- a/LayoutTests/fast/css/script-tests/background-clip-text.js
+++ b/LayoutTests/fast/css/script-tests/background-clip-text.js
@@ -8,29 +8,29 @@ function test(declaration, property)
     var div = document.createElement("div");
     div.setAttribute("style", declaration);
     document.body.appendChild(div);
-    
+
     var result = div.style.getPropertyValue(property);
     document.body.removeChild(div);
     return result;
 }
 shouldBe('test("background-clip: -webkit-text", "background-clip")', '"-webkit-text"');
-shouldBe('test("background-clip: -webkit-text", "-webkit-background-clip")', 'null');
+shouldBeEqualToString('test("background-clip: -webkit-text", "-webkit-background-clip")', '');
 
 shouldBe('test("background-clip: content-box", "background-clip")', '"content-box"');
 shouldBe('test("background-clip: padding-box", "background-clip")', '"padding-box"');
 shouldBe('test("background-clip: border-box", "background-clip")', '"border-box"');
 
-shouldBe('test("background-clip: text", "background-clip")', 'null');
-shouldBe('test("background-clip: text", "-webkit-background-clip")', 'null');
+shouldBeEqualToString('test("background-clip: text", "background-clip")', '');
+shouldBeEqualToString('test("background-clip: text", "-webkit-background-clip")', '');
 
-shouldBe('test("-webkit-background-clip: -webkit-text", "background-clip")', 'null');
+shouldBeEqualToString('test("-webkit-background-clip: -webkit-text", "background-clip")', '');
 shouldBe('test("-webkit-background-clip: -webkit-text", "-webkit-background-clip")', '"-webkit-text"');
 
-shouldBe('test("-webkit-background-clip: text", "background-clip")', 'null');
+shouldBeEqualToString('test("-webkit-background-clip: text", "background-clip")', '');
 shouldBe('test("-webkit-background-clip: text", "-webkit-background-clip")', '"text"');
-shouldBe('test("background: url() padding-box", "-webkit-background-clip")', 'null');
+shouldBeEqualToString('test("background: url() padding-box", "-webkit-background-clip")', '');
 
-shouldBe('test("-webkit-mask: url() ", "background-clip")', 'null');
+shouldBeEqualToString('test("-webkit-mask: url() ", "background-clip")', '');
 shouldBe('test("background: url() ", "background-clip")', '"initial"');
 
 shouldBe('test("background: url() padding-box", "background-clip")', '"padding-box"');