code: protected boolean containsProperty(String alias) {
  		String k = resolveKey(alias);
  		return k == null ? false : resolver.containsProperty(k);
  	}
docs: Return whether the given property alias has at least one property key
  that is available for resolution, i.e., the value for the given key is
  not {@code null}.
  
  @param alias
  the property alias to resolve
  @return true if property exists, false otherwise