PCategoryDataTypeAdapterTest.java

    final GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeAdapter(PCategoryData.class, new PCategoryDataTypeAdapter());
    final Gson gson = gsonBuilder.create();

    String json = "{categories:[{value: \"\"}]}";
    PCityData pCityData = gson.fromJson(json, PCityData.class);

    ...

    static class PCityData {
        public List<PCategoryData> categories;
    }

    static class PCategoryData {
        public double value;
    }

    public class PCategoryDataTypeAdapter extends TypeAdapter<PCategoryData> {

        @Override
        public PCategoryData read(JsonReader in) throws IOException {
            final PCategoryData data = new PCategoryData();

            in.beginObject();
            while (in.hasNext()) {
                switch (in.nextName()) {
                    case "value":
                        try {
                            data.value = Double.valueOf(in.nextString());
                        } catch (NumberFormatException e) {
                            data.value = 0;
                        }
                        break;
                }
            }
            in.endObject();

            return data;
        }

        @Override
        public void write(JsonWriter out, PCategoryData data) throws IOException {
            out.beginObject();
            out.name("value").value(data.value);
            out.endObject();
        }
    }