Don't output style without values

src/domain_abstract/model/Styleable.js

@@ -95,7 +95,7 @@ export default {
       const imp = opts.important;
       const important = isArray(imp) ? imp.indexOf(prop) >= 0 : imp;
       const value = `${style[prop]}${important ? ' !important' : ''}`;
-      result.push(`${prop}:${value};`);
+      value && result.push(`${prop}:${value};`);
     }
 
     return result.join('');