code: public static @Nonnull Entry<String,JsonElement> field(String key, JsonElement value) {
          Entry<String, JsonElement> entry = new Entry<String,JsonElement>() {
  
              @Override
              public String getKey() {
                  return key;
              }
  
              @Override
              public JsonElement getValue() {
                  return value;
              }
  
              @Override
              public JsonElement setValue(JsonElement value) {
                  throw new UnsupportedOperationException("entries are immutable");
              }};
              return entry;
      }
docs: Create a new field that can be added to a JsonObject.
  @param key key
  @param value value
  @return field entry implementation that can be added to a JsonObject