code: @Nullable
    public Long getLong(@Nonnull String field) {
      Number number = (Number) get(field);
      return number == null ? null : number.longValue();
    }
docs: Returns the value of the field as a long.
  
  @param field The path to the field.
  @throws RuntimeException if the value is not a Number.
  @return The value of the field.