anchor.diff:    Result := (FValue = Null);
   end;
   
  +procedure TmQueryParameter.Assign(aValue: TNullableString);
  +begin
  +  if aValue.IsNull then
  +    Self.SetNull
  +  else
  +    Self.AsString:= aValue.Value;
  +end;
  +
  +procedure TmQueryParameter.Assign(aValue: TNullableInteger);
  +begin
  +  if aValue.IsNull then
  +    Self.SetNull
  +  else
  +    Self.AsInteger:= aValue.Value;
  +end;
  +
  +procedure TmQueryParameter.Assign(aValue: TNullableDateTime);
  +begin
  +  if aValue.IsNull then
  +    Self.SetNull
  +  else
  +    Self.AsDateTime:= aValue.Value;
  +end;
  +
  +procedure TmQueryParameter.Assign(aValue: TNullableDouble);
  +begin
  +  if aValue.IsNull then
  +    Self.SetNull
  +  else
  +    Self.AsFloat:= aValue.Value;
  +end;
  +
   
   function TmDatabaseConnectionInfo.GetDatabaseName: String;
   begin
  
positive.code: 
      procedure SetNull;
      function IsNull : boolean;
      property Name : String read FName write FName;
      property DataType : TmParameterDataType read GetParameterDataType write SetParameterDataType;
      property AsString : String read GetAsString write SetAsString;
  
negative.code: interface
  
  uses
    DB, Contnrs, SysUtils,
    mNullables;
  
  type
    TmDataConnectionException = class (Exception);
  