Merge branch 'release-3.4.0' of github.com:browserstack/a11y-engine-axe-core into release-3.4.0

Author: mattscepter

lib/checks/color/link-in-text-block-evaluate.js

@@ -136,6 +136,14 @@ function getColorContrast(node, parentBlock) {
   nodeColor = getForegroundColor(node);
   parentColor = getForegroundColor(parentBlock);
 
+  if (!nodeColor) {
+    nodeColor = new axe.commons.color.Color(0, 0, 0, 0);
+  }
+
+  if (!parentColor) {
+    parentColor = new axe.commons.color.Color(0, 0, 0, 0);
+  }
+
   if (!nodeColor || !parentColor) {
     return undefined;
   }