Firebase AuthResult on task shows cannot resolve symbol
<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>