#vulnerable code 
                             @Transactional(propagation=Propagation.REQUIRED, readOnly=false)
	public SpringUser<ID> loginWithNonce(@Valid NonceForm<ID> nonce, HttpServletResponse response) {
		
		U user = userRepository.findById(nonce.getUserId())
			.orElseThrow(MultiErrorException.supplier(
				"com.naturalprogrammer.spring.userNotFound"));

		if (user.getNonce().equals(nonce.getNonce())) {
			
			user.setNonce(null);
			userRepository.save(user);
			
			jwtService.addJwtAuthHeader(response, user.getId().toString(), properties.getJwt().getExpirationMilli());
			return user.toSpringUser();
		}
		
		throw MultiErrorException.supplier("com.naturalprogrammer.spring.invalidNonce").get();
	} 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Transactional(propagation=Propagation.REQUIRED, readOnly=false)
	public SpringUser<ID> loginWithNonce(@Valid NonceForm<ID> nonce, HttpServletResponse response) {
		
		U user = userRepository.findById(nonce.getUserId())
			.orElseThrow(MultiErrorException.supplier(
				"com.naturalprogrammer.spring.userNotFound"));

		if (user.getNonce().equals(nonce.getNonce())) {
			
			user.setNonce(null);
			userRepository.save(user);
			
			jwtService.addJwtAuthHeader(response, user.toSpringUser().getUsername(), properties.getJwt().getExpirationMilli());
			return user.toSpringUser();
		}
		
		throw MultiErrorException.supplier("com.naturalprogrammer.spring.invalidNonce").get();
	}