Firebase field names are automatically changed?

Hello firebase started automatically changing my field names, this creates a big problem

How can I solve this problem:

My Class

    public class TUser {
        private String UserKey;
        private String LicenceKey;
        private String UserName;
        private Boolean Active;
        private String LoginDateTime;
        private String InstanceId;
        private String AcenteAdi;
        private String Version;
        private String MethodName;

        public TUser() {
        }

        public TUser(String userKey, String licenceKey, String userName, Boolean active, String loginDateTime, String instanceId, String acenteAdi, String version, String methodName) {
            UserKey = userKey;
            LicenceKey = licenceKey;
            UserName = userName;
            Active = active;
            LoginDateTime = loginDateTime;
            InstanceId = instanceId;
            AcenteAdi = acenteAdi;
            Version = version;
            MethodName = methodName;
        }

// ************ get set etc ****

    }

I have Changed minifyEnabled from true to false in build.gradle(module)

minifyEnabled: false

and That works for me...!