google/gson · warning · UnsupportedOperationException

String value is empty

Error message

String value is empty

What it means

JsonPrimitive.getAsCharacter() (deprecated) returns the first char of the stored string; if the string is empty there is no character to return, so it throws UnsupportedOperationException. The deprecation note says the method is misleading (it is not a real char coercion).

Source

Thrown at gson/src/main/java/com/google/gson/JsonPrimitive.java:253

  /**
   * @throws NumberFormatException {@inheritDoc}
   */
  @Override
  public byte getAsByte() {
    return isNumber() ? getAsNumber().byteValue() : Byte.parseByte(getAsString());
  }

  /**
   * @throws UnsupportedOperationException if the string value of this primitive is empty.
   * @deprecated This method is misleading, as it does not get this element as a char but rather as
   *     a string's first character.
   */
  @Deprecated
  @Override
  public char getAsCharacter() {
    String s = getAsString();
    if (s.isEmpty()) {
      throw new UnsupportedOperationException("String value is empty");
    } else {
      return s.charAt(0);
    }
  }

  /** Returns the hash code of this object. */
  @Override
  public int hashCode() {
    if (value == null) {
      return 31;
    }
    // The conditions below parallel the structure of equals(Object). Unlike in equals, every
    // numeric branch must delegate to the same double-based hash: equals can consider primitives
    // from *different* branches equal (for example Integer 42 equals Double 42.0 and a lazily
    // parsed number 42 through the floating-point comparison), so a branch hashing anything other
    // than the double value would give equal primitives different hash codes, see
    // https://github.com/google/gson/issues/992
    if (isIntegral(this)) {

View on GitHub (pinned to 8b8628c656)

Solutions

1. Stop using the deprecated getAsCharacter(); use getAsString() and handle length explicitly.
2. Guard with if (!s.isEmpty()) charAt(0);
3. Replace char handling with String throughout to avoid the single-char assumption.

Example fix

// before (deprecated)
char c = prim.getAsCharacter();

// after
String s = prim.getAsString();
char c = s.isEmpty() ? '\0' : s.charAt(0);

String s = prim.getAsString();
if (s.isEmpty()) return /* default */;

boolean hasChar(JsonPrimitive p) {
  return p.isString() && !p.getAsString().isEmpty();
}

try {
  char c = prim.getAsCharacter();
} catch (UnsupportedOperationException ex) {
  c = '\0';
}

When it happens

Trigger: Calling getAsCharacter() on a JsonPrimitive built from "" or parsed from a JSON empty string "".

Common situations: Legacy code still using the deprecated method; APIs that return empty strings for optional char-like fields; data migration leaving empty placeholders.

Related errors

• Primitive is neither a number nor a string
• JsonReader is closed
• Custom JsonElement subclass {className} is not supported
• Expected {expected} but was {peek}{location}
• Expected STRING but was {token}{location}

AI-assisted analysis of google/gson@8b8628c656 (2026-08-04). Data as JSON: /data/errors/0e3c1b3363f7d4c9.json. Report an issue: GitHub.