Access violation reading location 0xFFFFFFFFFFFFFFFF code example

Example: read access violation. _Pnext was 0xFFFFFFFFFFFFFFFF.

if (this->loginbuttons["Login"]->isclicked()) {

		std::string name = this->key["username"]->getText();
		std::string password = this->key["password"]->getText();
		
		password = enc.Encrypt_Data(password);


		for (auto& it : this->key) {

			it.second->set_RequiredError();
		}

		//if (this->key["username"]->Check_requirements() && this->key["password"]->Check_requirements()) {

			this->quer["login"] = new Query(std::ostringstream().flush() << "SELECT * FROM accounts WHERE username=Bruh AND password=Bruh LIMIT 1" , this->con->get_Connection());


			if (this->quer["login"]->string_Res() != "") {

			

					this->states->push(new MainMenu(this->window, this->keys, this->states));
					std::cout << "Logged in";

				
	
			}

			else {

				std::cout << "Inccorect Password or Username!";
			}
		//}
	}	
}