google/gson · error · JsonSyntaxException

Invalid bitset value type: ${tokenType}; at path ${path}

Error message

Invalid bitset value type: ${tokenType}; at path ${path}

What it means

The BitSet adapter handles NUMBER, STRING, and BOOLEAN token types. If an array element is any other JSON token type (NULL, BEGIN_OBJECT, BEGIN_ARRAY), it falls through to the default case and throws JsonSyntaxException identifying the unexpected token type.

Source

Thrown at gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java:122

              case STRING:
                int intValue = in.nextInt();
                if (intValue == 0) {
                  set = false;
                } else if (intValue == 1) {
                  set = true;
                } else {
                  throw new JsonSyntaxException(
                      "Invalid bitset value "
                          + intValue
                          + ", expected 0 or 1; at path "
                          + in.getPreviousPath());
                }
                break;
              case BOOLEAN:
                set = in.nextBoolean();
                break;
              default:
                throw new JsonSyntaxException(
                    "Invalid bitset value type: " + tokenType + "; at path " + in.getPath());
            }
            if (set) {
              bitset.set(i);
            }
            ++i;
            tokenType = in.peek();
          }
          in.endArray();
          return bitset;
        }

        @Override
        public void write(JsonWriter out, BitSet src) throws IOException {
          out.beginArray();
          for (int i = 0, length = src.length(); i < length; i++) {
            int value = src.get(i) ? 1 : 0;
            out.value(value);

View on GitHub (pinned to 310ac341f2)

Solutions

1. Validate the JSON array structure before deserialization — ensure every element is a number, string, or boolean
2. Clean or reject malformed input at the API boundary
3. Register a custom TypeAdapter<BitSet> that tolerates and skips null elements

Example fix

// before
gson.fromJson("[1, null, 0]", BitSet.class); // throws — NULL token

// after — strip nulls from the array before deserializing
JsonArray arr = JsonParser.parseString("[1, null, 0]").getAsJsonArray();
arr.removeIf(JsonNull.class::isInstance);
BitSet bs = gson.fromJson(arr, BitSet.class);

// Validate BitSet array element types before deserializing
public static void validateBitSetTypes(JsonArray arr) {
    for (JsonElement e : arr) {
        if (!e.isJsonPrimitive()) {
            throw new IllegalArgumentException(
                "Invalid bitset element type: " + e + " (expected number, string, or boolean)");
        }
        var p = e.getAsJsonPrimitive();
        if (!p.isNumber() && !p.isString() && !p.isBoolean()) {
            throw new IllegalArgumentException("Invalid bitset element: " + e);
        }
    }
}

try {
    BitSet bs = gson.fromJson(json, BitSet.class);
} catch (JsonSyntaxException e) {
    if (e.getMessage().contains("Invalid bitset value type")) {
        // filter out null or non-primitive elements before retrying
    }
}

When it happens

Trigger: Deserialifying a JSON array containing null, an object, or a nested array into a BitSet field, e.g. [1, null, 0] or [1, {}, 0].

Common situations: Malformed API responses; schema mismatch where a bitset field receives mixed types; upstream serialization bug producing nulls in a bitset array.

Related errors

• Invalid bitset value ${intValue}, expected 0 or 1; at path $
• Expecting character, got: ${str}; at ${path}
• cannot deserialize ${baseType} because it does not define a
• cannot deserialize ${baseType} subtype named ${label}; did y
• Failed to parse date [${input}]: ${fail.getMessage()}

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/a10eee16147390c8. Report an issue: GitHub.