_decodeFormValue(formValue) {
    if (Array.isArray(formValue)) {
      return formValue
        .filter(item => typeof item === "string")
        .map(item => stringToPDFString(item));
    } else if (formValue instanceof Name) {
      return stringToPDFString(formValue.name);
    } else if (typeof formValue === "string") {
      return stringToPDFString(formValue);
    }
    return null;
  }
Decode the given form value.

@private
@memberof WidgetAnnotation
@param {Array<string>|Name|string} formValue - The (possibly encoded)
  form value.
@returns {Array<string>|string|null}