private static Object serialize()

in firebase-firestore/src/main/java/com/google/firebase/firestore/util/CustomClassMapper.java [108:180]
73 lines of code
26 McCabe index (conditional complexity)

  private static <T> Object serialize(T o, ErrorPath path) {
    if (path.getLength() > MAX_DEPTH) {
      throw serializeError(
          path,
          "Exceeded maximum depth of "
              + MAX_DEPTH
              + ", which likely indicates there's an object cycle");
    }
    if (o == null) {
      return null;
    } else if (o instanceof Number) {
      if (o instanceof Long || o instanceof Integer || o instanceof Double || o instanceof Float) {
        return o;
      } else {
        throw serializeError(
            path,
            String.format(
                "Numbers of type %s are not supported, please use an int, long, float or double",
                o.getClass().getSimpleName()));
      }
    } else if (o instanceof String) {
      return o;
    } else if (o instanceof Boolean) {
      return o;
    } else if (o instanceof Character) {
      throw serializeError(path, "Characters are not supported, please use Strings");
    } else if (o instanceof Map) {
      Map<String, Object> result = new HashMap<>();
      for (Map.Entry<Object, Object> entry : ((Map<Object, Object>) o).entrySet()) {
        Object key = entry.getKey();
        if (key instanceof String) {
          String keyString = (String) key;
          result.put(keyString, serialize(entry.getValue(), path.child(keyString)));
        } else {
          throw serializeError(path, "Maps with non-string keys are not supported");
        }
      }
      return result;
    } else if (o instanceof Collection) {
      if (o instanceof List) {
        List<Object> list = (List<Object>) o;
        List<Object> result = new ArrayList<>(list.size());
        for (int i = 0; i < list.size(); i++) {
          result.add(serialize(list.get(i), path.child("[" + i + "]")));
        }
        return result;
      } else {
        throw serializeError(
            path, "Serializing Collections is not supported, please use Lists instead");
      }
    } else if (o.getClass().isArray()) {
      throw serializeError(path, "Serializing Arrays is not supported, please use Lists instead");
    } else if (o instanceof Enum) {
      String enumName = ((Enum<?>) o).name();
      try {
        Field enumField = o.getClass().getField(enumName);
        return BeanMapper.propertyName(enumField);
      } catch (NoSuchFieldException ex) {
        return enumName;
      }
    } else if (o instanceof Date
        || o instanceof Timestamp
        || o instanceof GeoPoint
        || o instanceof Blob
        || o instanceof DocumentReference
        || o instanceof FieldValue) {
      return o;
    } else {
      Class<T> clazz = (Class<T>) o.getClass();
      BeanMapper<T> mapper = loadOrCreateBeanMapperForClass(clazz);
      return mapper.serialize(o, path);
    }
  }