code: public static CFuncRef from(String def) {
      if (def == null || def.isEmpty()) {
        return NOP;
      }
      String[] parts = def.split("=");
      assert parts.length == 2 : "Input should be `lang:key=funcName`";
      String[] langParts = parts[0].split(":");
      assert langParts.length == 2 : "Input should be `lang:key=funcName`";
      return new CFuncRef(langParts[0], langParts[1], parts[1]);
    }
docs: Create function definition from "lang:keyName=funcName"
  
  @param def  function definition
  @return instance of function of NOP if definition is wrong