如何为imgUri实现条件语句

Question

任何人都可以帮助诊断此问题吗？我是android studio的新手，正在尝试一个新项目，该项目需要用户输入并将其粘贴到Firebase数据库中。问题是，直到我引入了Firebase Store为止，一切都运转良好。现在，当我输入用户数据而不附加图像时，该应用程序将崩溃。错误显示Attempt to invoke virtual method 'java.lang.String com.google.firebase.storage.StorageReference.toString()' on a null object reference

public class Signup extends AppCompatActivity {

    private EditText inputEmail, inputPassword, confirmPassword;
    private FirebaseAuth mAuth;
    private Button btnRegister;
    private EditText nameEt;
    private EditText phoneNumberEt;
    private EditText userNameEt;
    private LinearLayout uploadPhoto;
    DatabaseReference databaseReference;
    //FirebaseStorage mStorageRef;
    StorageReference mStorageRef;
    FirebaseDatabase database;
    ImageView profilephoto;


    private ProgressDialog PD;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private String name, userName, phoneNumber;
    public static final int REQUEST_CODE = 1234;
    Uri imgUri;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);        setContentView(R.layout.activity_signup);

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    setTitle("Sign Up");
    mAuth = FirebaseAuth.getInstance();
    PD = new ProgressDialog(Signup.this);
    database = FirebaseDatabase.getInstance();

    databaseReference = database.getReference("User").child("Clients");

    inputEmail = (EditText) findViewById(R.id.inputEmail);
    inputPassword = (EditText) findViewById(R.id.inputPassword);
    confirmPassword = (EditText) findViewById(R.id.confirmPassword);
    btnRegister = (Button) findViewById(R.id.register);
    nameEt = (EditText) findViewById(R.id.nameEt);
    phoneNumberEt = (EditText) findViewById(R.id.phoneNumberEt);
    userNameEt = (EditText) findViewById(R.id.userNameEt);
    uploadPhoto = (LinearLayout) findViewById(R.id.uploadPhoto);
    profilephoto = (ImageView) findViewById(R.id.profilephoto);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if ((requestCode == REQUEST_CODE) && resultCode == RESULT_OK && data != null && data.getData() != null) {
    imgUri = data.getData();
    profilephoto.setImageURI(imgUri);
    mStorageRef = FirebaseStorage.getInstance().getReference().child("images/" + System.currentTimeMillis() + " " + getImageExt(imgUri)).child(imgUri.getLastPathSegment());


    try {Bitmap bm = MediaStore.Images.Media.getBitmap(getContentResolver(), imgUri);
    ImageView profilephoto = (ImageView) findViewById(R.id.profilephoto);
    profilephoto.setImageBitmap(bm);
    } catch (IOException e) {
    e.printStackTrace();
    }
    }
    }

    public String getImageExt(Uri uri) {
    ContentResolver contentResolver = getContentResolver();
    MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
    return mimeTypeMap.getExtensionFromMimeType(contentResolver.getType(uri));
    }

    public void btnUpload_Click(View view) {
    final String name = nameEt.getText().toString().trim();
    final String password = inputPassword.getText().toString().trim();
    final String email = inputEmail.getText().toString().trim();
    final String cnfirmpassword =confirmPassword.getText().toString().trim();
    final String phoneNumber = phoneNumberEt.getText().toString().trim();
    final String imageaddress = mStorageRef.toString();

    if (imageaddress!=null &&!name.isEmpty() && !password.isEmpty() && !email.isEmpty() && !cnfirmpassword.isEmpty() && !phoneNumber.isEmpty()) {
    PD.setMessage("Signing up...");
    PD.show();

    mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
    @Override
    public void onComplete(@NonNull Task<AuthResult> task) {
    if (task.isSuccessful()) {
    String user_id = mAuth.getCurrentUser().getUid();
    DatabaseReference user_Details = databaseReference.child(user_id);
    user_Details.child("name").setValue(name);
    user_Details.child("email").setValue(email);                        user_Details.child("phonenumber").setValue(phoneNumber);                 user_Details.child("imageAddress").setValue(imageaddress);

    mStorageRef.putFile(imgUri).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
    @Override
    public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
    Toast.makeText(getApplicationContext(), "Image uploaded", Toast.LENGTH_LONG).show();
    PD.dismiss();
    Intent intent = new Intent(Signup.this, Login.class);                               intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    startActivity(intent);
    }
    })
    .addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception e) {                                      Toast.makeText(getApplicationContext(), "Upload failed: " + e.getMessage(), Toast.LENGTH_LONG).show();
    }
    })
    .addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>(){
    @Override
    public void onProgress(UploadTask.TaskSnapshot taskSnapshot) {
    PD.show();
    }});
    } else if (!task.isSuccessful()) {
    Toast.makeText(getApplicationContext(), "User already exist", Toast.LENGTH_LONG).show();
    PD.dismiss();
    }
    }
    });
    }
    else if (name.isEmpty()) {
    // If sign in fails, display a message to the user.
    Toast.makeText(Signup.this, "Please Enter Name", Toast.LENGTH_SHORT).show();
    } else if (password.length() < 6) {
    Toast.makeText(Signup.this, "Please Enter Password", Toast.LENGTH_SHORT).show();
    } else if (!password.equals(cnfirmpassword)) {
    Toast.makeText(Signup.this, "Password do not match", Toast.LENGTH_SHORT).show();
    } else if (phoneNumber.isEmpty()) {
    Toast.makeText(Signup.this, "Please enter phone number", Toast.LENGTH_SHORT).show();
    } else if (cnfirmpassword.isEmpty()) {
    Toast.makeText(Signup.this, "Please confirm password", Toast.LENGTH_SHORT).show();
    }}

    public void onClick1 (View view) {
    Intent intent = new Intent();
    intent.setType("image/*");enter code here
    intent.setAction(Intent.ACTION_GET_CONTENT);
    startActivityForResult(Intent.createChooser(intent, "Select image"), REQUEST_CODE);
    }
}

谢谢。