code: public function getValue($entity)
      {
          if (null === $this->getter) {
              // FIXXME Improve this message
              throw new \Exception(
                  "Can't get the entity's {$this->name} property as no getter has been found."
              );
          } elseif (false === ($entity instanceof $this->class)) {
              // FIXXME Improve this message
              throw new \Exception(
                  "Can't get the entity's {$this->name} property as the entity is not an instance of {$this->class}."
              );
          }
  
          if (self::GETTER_SETTER_METHOD === $this->getterType) {
              return $entity->{$this->getter}();
          } else {
              return $entity->{$this->getter};
          }
      }
docs: Gets this property's value of the given entity
  
  @param object $entity The entity.
  
  @return mixed The property's value.