code: public function add($value)
      {
          $value = Cast::Float($value);
  
          if ($this->value === null) {
              return new FloatType($this->value);
          }
  
          return new FloatType($this->value + $value);
      }
docs: Addition. Product is always FloatType.
  
  @param  mixed $value
  @return FloatType