public function optional(string $alias, string $type): EntityDefinitionOptions {
    return $this->optional[$alias] = new EntityDefinitionOptions($alias, $type);
  }
public function optional(string $alias, string $type): EntityDefinitionOptions {
    return $this->optional[$alias] = new EntityDefinitionOptions($alias, $type);
  }
public function optional ( string $ alias , string $ type ) : EntityDefinitionOptions { return $ this -> optional [ $ alias ] = new EntityDefinitionOptions ( $ alias , $ type ) ; }
Adds an optional column

@param  string  $alias  The name of the column (does not have to match the database)
@param  string  $type   A value object class name

@return  EntityDefinitionOptions  Options for the column
Adds an optional column