google/gson · error · JsonSyntaxException

Invalid bitset value type: " + tokenType + "; at path " + in

Error message

Invalid bitset value type: " + tokenType + "; at path " + in.getPath()

What it means

The BitSet TypeAdapter expects each element to be NUMBER, STRING, or BOOLEAN; any other JSON token (NULL, BEGIN_OBJECT, BEGIN_ARRAY, NAME) triggers JsonSyntaxException with the token type and current path. Essentially the array element is structurally wrong, not just out of range.

Source

Thrown at gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java:120

              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 8b8628c656)

Solutions

Filter out or replace null/nested elements in the source JSON before deserialization.
Change the target type to a List<Object> or List<Integer> if the structure is genuinely heterogeneous.
Register a custom TypeAdapter<BitSet> that tolerates null (treats as 0).
Validate the JSON shape (array of scalars only) at the trust boundary.

Example fix

// before
BitSet b = gson.fromJson("[0,null,1]", BitSet.class); // throws

// after
JsonArray a = JsonParser.parseString(json).getAsJsonArray();
BitSet bs = new BitSet();
for (int i=0;i<a.size();i++) if (!a.get(i).isJsonNull() && a.get(i).getAsBoolean()) bs.set(i);

Defensive patterns

Strategy: validation

Validate before calling

// Ensure BitSet array elements are NUMBER/STRING/BOOLEAN only
for (JsonElement e : arr) {
  if (e.isJsonNull() || e.isJsonObject() || e.isJsonArray()) {
    throw new IllegalArgumentException("Bad bitset element type: " + e);
  }
}

Type guard

null

Try / catch

try {
  gson.fromJson(json, BitSet.class);
} catch (JsonSyntaxException e) {
  if (e.getMessage().startsWith("Invalid bitset value type")) {
    // filter out null/nested elements and retry
  } else throw e;
}

Prevention

Validate JSON shape (flat array of scalars) before deserializing into BitSet.
Switch to a tolerant custom adapter if nulls are expected.
Keep schema validation at the trust boundary.

When it happens

Trigger: Deserializing a JSON array containing null, a nested object, or another array into a BitSet field; feeding malformed JSON where a BitSet is expected. Triggered at line 120 in the default branch of the switch.

Common situations: API responses that include `null` placeholders in flag arrays; nested structures where a BitSet was mistakenly declared; partially-typed schema changes; corrupt/attacker-supplied JSON.

Related errors

AI-assisted analysis of google/gson@8b8628c656 (2026-08-04). Data as JSON: /data/errors/82cdcd027f91b612.json. Report an issue: GitHub.