title: Realtime database doesn't work on firebase
body: <p>I'm new in Android app development and making an application on Android Studio.</p>
  
  <p>Can check the user list from Authentication tab on firebase after I made an account, but Realtime Database doesn't work and can't get any data.</p>
  
  <p>Here is my <code>Registration Activity</code> file's realtime database part code.
  Please let me know what the problem is.</p>
  
  <pre><code>mRegistration.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
          final String email = mEmail.getText().toString();
          final String password = mPassword.getText().toString();
          final String name = mName.getText().toString();
          mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener((Executor) getApplication(), new OnCompleteListener&lt;AuthResult&gt;() {
              @Override
              public void onComplete(@NonNull Task&lt;AuthResult&gt; task) {
                  if (!task.isSuccessful()) {
                      Toast.makeText(getApplication(), "로그인 실패!", Toast.LENGTH_SHORT).show();
                  } else {
                      String userId = mAuth.getCurrentUser().getUid();
                      DatabaseReference currentUserDB = FirebaseDatabase.getInstance().getReference().child("users").child(userId);
  
                      Map userInfo = new HashMap&lt;&gt;();
                      userInfo.put("email", email);
                      userInfo.put("name", name);
                      userInfo.put("profileImageUrl", "default");
  
                      currentUserDB.updateChildren(userInfo);
                  }
              }
          });
      }
  });
  </code></pre>
  
  <p>The database:</p>
  
  <p><img src="https://i.imgur.com/f0l8BGP.png" alt=""></p>