#vulnerable code 
                                @Override
    public OAuthGrant getById(Long grantId) {
        OAuthGrant grant = find(grantId);
        grant = restoreRefs(grant, null, null);
        return grant;
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public OAuthGrant getById(Long grantId) {
        OAuthGrant grant = find(grantId);
        if( grant != null) {
            grant = restoreRefs(grant, null, null);
        }
        return grant;
    }