从Firebase中删除值：空指针异常

Question

我正在尝试从Firebase删除子字符串，但是我不断收到错误Attempting to invoke method on a null object reference。删除子项的代码行是：

DatabaseLike.child(uploadCurrent.getName()).child(mAuth.getCurrentUser().getUid()).removeValue();

完整的方法是这样的：

  public void onBindViewHolder(final ImageViewHolder holder, final int 
  position) {
//database reference
    mDatabaseRef = FirebaseDatabase.getInstance().getReference("likes");
    //mCurrentUserId = mAuth.getCurrentUser().getUid();
    mAuth = FirebaseAuth.getInstance();

    final UploadClass uploadCurrent = mUploads.get(position);
    //new code 10/1/2019
    //final String post_key = mUploads.get(position).toString();
    //end
    holder.textViewName.setText(uploadCurrent.getName());
    Picasso.with(mContext)
            .load(uploadCurrent.getImageUrl())
            .placeholder(R.mipmap.ic_launcher)
            .fit()
            .centerCrop()
            .into(holder.imageView);

    holder.imageView.setOnClickListener(new View.OnClickListener(){
       @Override
       public void onClick(View v){
          Toast.makeText(mContext, uploadCurrent.getName(), 
 Toast.LENGTH_LONG).show();
       }
    });
    holder.mLikebtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            mProcessLike = true;


            mDatabaseRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) 
{
                    if (mProcessLike) {

                        if (dataSnapshot.child(uploadCurrent.getName()).hasChild(mAuth.getCurrentUser().getUid())) {
                            //Cant use unlike as it is string value
                            mDatabaseLike.child(uploadCurrent.getName()).child(mAuth.getCurrentUser().getUid()).removeValue();

                            mProcessLike = false;

                        } else {

                            mDatabaseRef.child(uploadCurrent.getName()).child(mAuth.getCurrentUser().getUid()).setValue("Like");

                            mProcessLike = false;
                        }
                    }
                }

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

                }
            });