title: DatabaseException: No properties to serialize found on class
body: <p>I'm getting error <code>com.google.firebase.database.DatabaseException: No properties to serialize found on class com.example.journyabode.detailsofUser</code>.
  I've tried changing <code>proguard</code> rules but still I'm not getting</p>
  
  <pre><code>public class User_Details extends AppCompatActivity {
  
      EditText F_name,L_Name,Mobile,address;
      Button update;
  
      private FirebaseAuth mAuth;
      private String user;
      private DatabaseReference myref;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate (savedInstanceState);
          setContentView (R.layout.activity_user_details);
  
          mAuth  =FirebaseAuth.getInstance ();
          user = mAuth.getCurrentUser ().getUid ();
          myref = FirebaseDatabase.getInstance ().getReference ("Users");
  
  
          if(mAuth.getCurrentUser ()== null){
              finish ();
              startActivity (new Intent (this,Login.class));
          }
  
          F_name = (EditText)findViewById (R.id.F_Name);
          L_Name = (EditText)findViewById (R.id.L_Name);
          Mobile = (EditText)findViewById (R.id.Phone);
          address = (EditText)findViewById (R.id.Address);
          update = (Button)findViewById (R.id.update);
  
          update.setOnClickListener (new View.OnClickListener () {
              @Override
              public void onClick(View view) {
  
                  String First_Name = F_name.getText ().toString ().trim ();
                  String Last_Name = L_Name.getText ().toString ().trim ();
                  String phone = Mobile.getText ().toString ().trim ();
                  String addres = address.getText ().toString ().trim ();
  
  
                  if (TextUtils.isEmpty (First_Name)) {
                      Toast.makeText (User_Details.this, "Please Enter First To continue", Toast.LENGTH_SHORT).show ();
                      return;
                  }
                  if (TextUtils.isEmpty (Last_Name)) {
                      Toast.makeText (User_Details.this, "Plaese Enter Last Name ", Toast.LENGTH_SHORT).show ();
                      return;
                  }
                  if (TextUtils.isEmpty (phone)) {
                      Toast.makeText (User_Details.this, "Please Enter Phone Number", Toast.LENGTH_SHORT).show ();
                      return;
                  }
                  if (TextUtils.isEmpty (addres)) {
                      Toast.makeText (User_Details.this, "Please Enter address to continue", Toast.LENGTH_SHORT).show ();
                      return;
                  }
  
  
                      detailsofUser userDetail = new detailsofUser (First_Name, Last_Name, phone, addres);
  
                      FirebaseUser user = mAuth.getCurrentUser ();
  
                      myref.child (user.getUid ()).setValue (userDetail);
                      Intent intent = new Intent (User_Details.this,Homepage.class);
                      startActivity (intent);
  
                      Toast.makeText (User_Details.this, "Details_Saved", Toast.LENGTH_SHORT).show ();
  
                  }
  
          });
      }
  }
  </code></pre>
  
  <p>Logcat:</p>
  
  <pre><code>2019-02-23 00:32:45.205 27516-27516/? E/Zygote: isWhitelistProcess - Process is Whitelisted
  2019-02-23 00:32:45.205 27516-27516/? E/libpersona: scanKnoxPersonas
  2019-02-23 00:32:45.206 27516-27516/? E/libpersona: Couldn't open the File - /data/system/users/0/personalist.xml - No such file or directory
  2019-02-23 00:32:53.426 27516-27516/com.example.journyabode E/AndroidRuntime: FATAL EXCEPTION: main
      Process: com.example.journyabode, PID: 27516
      com.google.firebase.database.DatabaseException: No properties to serialize found on class com.example.journyabode.detailsofUser
          at com.google.android.gms.internal.firebase_database.zzku.&lt;init&gt;(Unknown Source:761)
          at com.google.android.gms.internal.firebase_database.zzkt.zza(Unknown Source:12)
          at com.google.android.gms.internal.firebase_database.zzkt.zzi(Unknown Source:249)
          at com.google.android.gms.internal.firebase_database.zzkt.zzh(Unknown Source:0)
          at com.google.firebase.database.DatabaseReference.zza(Unknown Source:10)
          at com.google.firebase.database.DatabaseReference.setValue(Unknown Source:7)
          at com.example.journyabode.User_Details$1.onClick(User_Details.java:81)
          at android.view.View.performClick(View.java:6993)
          at android.widget.TextView.performClick(TextView.java:12752)
          at android.view.View$PerformClick.run(View.java:26509)
          at android.os.Handler.handleCallback(Handler.java:790)
          at android.os.Handler.dispatchMessage(Handler.java:99)
          at android.os.Looper.loop(Looper.java:164)
          at android.app.ActivityThread.main(ActivityThread.java:7025)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:441)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)
  </code></pre>