message: Use empty string as flag to remove attribute instead of null
diff: @@ -160,7 +160,7 @@ function setProps(element: Element, props: {}) {
  function mergeProps(a:{}, b:{}) :{} {
  const props = [];
  - if(a) Object.keys(a).forEach(p=>props[p]=null);
  + if(a) Object.keys(a).forEach(p=>props[p]='');
  if(b) Object.keys(b).forEach(p=>props[p]=b[p]);
  return props;
  }
  