when i activate proguard i didnot get previous data from firebase realtime in androidstudio

Question

I am using firebase realtime but when i released new update with progurad activate

 minifyEnabled true
        shrinkResources true
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        signingConfig signingConfigs.release

data not showing when i get data from firebase to a Groups model

  for (DataSnapshot childSnap : snapshot.getChildren()) {
                                  //  Log.i("data",""+childSnap.getValue(Groups.class)+"      ");
                                    Groups groups = childSnap.getValue(Groups.class);
                                    GroupsArrayList.add(groups);
                                }

i dont know why i add rules but still data not showing in proguard-rules-pro

-keep class com.myapp.models.Groups.** { *; }

my model class

public class Groups {
String createdby;
String groupname;
String groupdescription;
String groupid;
String grouptype;
String createddatetime;
public Groups()
{

}

public Groups(String createdby, String groupname, String groupdescription, String groupid, String grouptype, String createddatetime) {
    this.createdby = createdby;
    this.groupname = groupname;
    this.groupdescription = groupdescription;
    this.groupid = groupid;
    this.grouptype = grouptype;
    this.createddatetime = createddatetime;
}