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