title: Firebase AuthResult on task shows cannot resolve symbol
body: <p>Getting red line over Task. I have imported <code>import com.google.firebase.auth.AuthResult;</code> too, yet it shows <code>cannot resolve symbol authresult</code> in that too.</p>
  
  <pre><code>    auth = FirebaseAuth.getInstance();
      sign_up_button = (Button) findViewById(R.id.sign_up_button);
      email = (EditText) findViewById(R.id.email);
      password = (EditText) findViewById(R.id.password);    
      sign_up_button.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              String email_a = email.getText().toString().trim();
              String password_a = password.getText().toString().trim();
              //create user
              auth.createUserWithEmailAndPassword(email_a, password_a)
                      .addOnCompleteListener(RegisterStaff.this, new OnCompleteListener&lt;AuthResult&gt;() {
                          @Override
                          public void onComplete(@NonNull Task&lt;AuthResult&gt; task) {
                              Toast.makeText(RegisterStaff.this, "Registration Complete..:" + task.isSuccessful(), Toast.LENGTH_SHORT).show();
                              progressBar.setVisibility(View.GONE);
                              // If sign in fails, display a message to the user. If sign in succeeds
                              // the auth state listener will be notified and logic to handle the
                              // signed in user can be handled in the listener.
                              if (!task.isSuccessful()) {
                                  Toast.makeText(RegisterStaff.this, "Registration failed..." + task.getException(),
                                          Toast.LENGTH_SHORT).show();
                              } else {
                                  startActivity(new Intent(RegisterStaff.this, StaffLogin.class));
                                  finish();
                              }
                          }
                      }
               );}
      });
  }
  @Override
  protected void onResume() {
      super.onResume();
      progressBar.setVisibility(View.GONE);
  }
  </code></pre>