Java firebase.auth.FirebaseUser.linkWithCredential引发空指针异常

我应该如何将现有用户帐户与不同的提供商链接，但却是同一封电子邮件？ 比如谷歌和Facebook

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如有任何建议，我们将不胜感激。谢谢。

mAuth.getCurrentUser（）

正在返回一个空的FirebaseUser，因为在调用它时没有用户登录。在调用FirebaseUser对象上的方法之前，您的代码应该对此进行检查，如显示的API文档所示。

但当我根据我的Logcat单击fbLoginBtn时，它已登录。示例中提到的方法只是通过firebase进行身份验证，在该身份验证过程中，它检测到用户使用相同的电子邮件退出。那么，如果存在使用相同电子邮件的其他提供程序，我应该如何处理提供程序链接呢？如果您注意到上面的方法handleFacebookAccessToken（），其中调用了onFailure方法。因为同一封电子邮件，但不同的提供商。

public void handleFacebookAccessToken(final AccessToken token, final Activity activity) {
        Log.d(TAG, "handleFacebookAccessToken: " + token);

        final AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(activity, new OnCompleteListener<AuthResult>() {

                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            Log.d(TAG, "signInWithCredential:success");
                            FirebaseUser user = mAuth.getCurrentUser();
                            authListener.updateSignedUI(user);
                        }
                    }
                }).addOnFailureListener(activity, new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.w(TAG, "signInWithCredential:failure", e);
                if (e instanceof FirebaseAuthUserCollisionException) {
                    handleLinkingFacebookUsers(credential, activity);
                }
            }
        });
    }

    private void handleLinkingFacebookUsers(AuthCredential savedFBCredential, Activity activity) {
        //AuthCredential credentialFacebook = FacebookAuthProvider.getCredential(token.getToken());
        //AuthCredential credentialGoogle = GoogleAuthProvider.getCredential(googleIdToken, null);
           mAuth.getCurrentUser()
                   .linkWithCredential(savedFBCredential)   // THIS LINE TROWS NULL POINTER EXCEPTION
                   .addOnCompleteListener(activity, new OnCompleteListener<AuthResult>() {
                       @Override
                       public void onComplete(@NonNull Task<AuthResult> task) {
                           if (task.isSuccessful()) {
                               Log.d(TAG, "linkWithCredential:success");
                               FirebaseUser user = task.getResult().getUser();
                               authListener.updateSignedUI(user);
                           } else {
                               Log.w(TAG, "linkWithCredential:failure", task.getException());
                               authListener.updateSignedUI(null);
                           }

                           // ...
                       }
                   });

    }

com.google.firebase.auth.FirebaseAuthUserCollisionException: An account already exists with the same email address but different sign-in credentials. Sign in using a provider associated with this email address.
        at com.google.firebase.auth.api.internal.zzdv.zza(com.google.firebase:firebase-auth@@19.2.0:42)
        at com.google.firebase.auth.api.internal.zzfc.zza(com.google.firebase:firebase-auth@@19.2.0:19)
        at com.google.firebase.auth.api.internal.zzes.zza(com.google.firebase:firebase-auth@@19.2.0:34)
        at com.google.firebase.auth.api.internal.zzeu.zza(com.google.firebase:firebase-auth@@19.2.0:98)
        at com.google.firebase.auth.api.internal.zzeu.zza(com.google.firebase:firebase-auth@@19.2.0:85)