code: public JsonWriter property(String key, Object value) throws IOException {
        Preconditions.checkArgument(!inArray(), "Cannot write a property inside an array.");
        writeName(key);
        value(value);
        return this;
     }
docs: Writes a  key value pair
  
  @param key   the key
  @param value the value
  @return This structured writer
  @throws IOException Something went wrong writing