intent.getStringExtra（）空指针异常

Question

不能为child（）中的参数'pathString'传递null

public class MessageActivity extends AppCompatActivity {


    CircleImageView profile_image;
    TextView username;

    FirebaseUser fuser;
    DatabaseReference reference;
    Intent intent;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message);

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
        profile_image = findViewById(R.id.profile_image);
        username = findViewById(R.id.username);

        intent = getIntent();
        String userid = intent.getStringExtra("userid");
        fuser = FirebaseAuth.getInstance().getCurrentUser();
        reference = FirebaseDatabase.getInstance().getReference("users").child(userid);

        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                User user = dataSnapshot.getValue(User.class);
                username.setText(user.getUsername());
                if(user.getImageURL().equals("defaults")){
                    profile_image.setImageResource(R.mipmap.ic_launcher);

                } else{
                    Glide.with(MessageActivity.this).load(user.getImageURL()).into(profile_image);
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

    }
}

原因：

intent = getIntent();
String userid = intent.getStringExtra("userid");

此代码始终为用户ID提供空值。