google/gson · warning · UnsupportedOperationException

String value is empty

Error message

String value is empty

What it means

Thrown by JsonPrimitive.getAsCharacter() (JsonPrimitive.java:253) as UnsupportedOperationException when the primitive's string value is empty — charAt(0) has nothing to return. The method is @Deprecated because it returns the first character of the string representation, not a true char conversion.

Solutions

1. Stop using the deprecated getAsCharacter(); read getAsString() and check length before charAt(0)
2. Guard with a non-empty check on the string value
3. Validate the source emits a single-character string for the field

Example fix

// before
char c = primitive.getAsCharacter(); // throws if value is ""
// after
String s = primitive.getAsString();
char c = s.isEmpty() ? '\0' : s.charAt(0);

JsonPrimitive p = ...;
String s = p.getAsString();
boolean hasChar = !s.isEmpty();

static Character firstCharOrNull(JsonPrimitive p) {
    String s = p.getAsString();
    return s.isEmpty() ? null : s.charAt(0);
}

try {
    char c = primitive.getAsCharacter();
} catch (UnsupportedOperationException ex) {
    // "String value is empty"
}

When it happens

Trigger: new JsonPrimitive("").getAsCharacter(); or a JSON string field that is empty being read as a char.

Common situations: Legacy code using the deprecated getAsCharacter(); empty/blank string fields where a single char was expected; config values left blank.

Related errors

• ${getClass().getSimpleName()}
• Primitive is neither a number nor a string
• Did not consume the entire document.
• Failed parsing JSON source
• Incomplete document

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/0e3c1b3363f7d4c9. Report an issue: GitHub.

Appendix: 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)) {

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