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

    mStorage = FirebaseStorage.getInstance().getReference();
    mDatabase = FirebaseDatabase.getInstance().getReference().child("Blog");


    mSelectImage = (ImageButton) findViewById(R.id.imageSelect);
    mPostTitle =(EditText)findViewById(R.id.titleField);
    mPostDesc = (EditText)findViewById(R.id.descField);
    mSubmitBtn = (Button)findViewById(R.id.submitBtn);

    grg = (RadioGroup) findViewById(R.id.gendField);
    grb = (RadioButton) findViewById(grg.getCheckedRadioButtonId());

    mProgress = new ProgressDialog(this);

    mSelectImage.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Intent galleryIntent = new Intent(Intent.ACTION_GET_CONTENT);
            galleryIntent.setType("image/*");
            startActivityForResult(galleryIntent,GALLERY_REQUEST);
        }
    });

    mSubmitBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            startposting();
        }
    });
}

private void startposting() {



    final String title_val = mPostTitle.getText().toString().trim();
    final String desc_val = mPostDesc.getText().toString().trim();
    final String gend_val = grb.getText().toString().trim();

    if(!TextUtils.isEmpty(title_val)&& !TextUtils.isEmpty(desc_val)&& mImageUri!=null){

        StorageReference filepath = mStorage.child("Blog_images").child(mImageUri.getLastPathSegment());

        filepath.putFile(mImageUri).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
            @Override
            public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {

                @SuppressWarnings("VisibleForTests") Uri downloadUri = taskSnapshot.getDownloadUrl();

                DatabaseReference newPost = mDatabase.push();
                newPost.child("title").setValue(title_val);
                newPost.child("desc").setValue(desc_val);
                newPost.child("image").setValue(downloadUri.toString());
                newPost.child("datetime").setValue(ServerValue.TIMESTAMP);

                newPost.child("gend").setValue(gend_val);


                mProgress.dismiss();

                startActivity(new Intent(PostActivity.this, MainActivity.class));
            }
        }).addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() {
            @Override
            public void onProgress(UploadTask.TaskSnapshot taskSnapshot) {
            @SuppressWarnings("VisibleForTests") double progress = (100.0 * taskSnapshot.getBytesTransferred()) / taskSnapshot.getTotalByteCount();


                mProgress.setMessage("Uploading " + ((int) progress) + "%...");
                mProgress.show();
            }
        });
    }


}

E/AndroidRuntime: FATAL EXCEPTION: main
                                                            Process: app.testfirebase, PID: 7995
                                                            java.lang.NullPointerException
                                                                at app.testfirebase.PostActivity.startposting(PostActivity.java:87)
                                                                at app.testfirebase.PostActivity.access$000(PostActivity.java:25)
                                                                at app.testfirebase.PostActivity$2.onClick(PostActivity.java:75)
                                                                at android.view.View.performClick(View.java:4438)
                                                                at android.view.View$PerformClick.run(View.java:18422)
                                                                at android.os.Handler.handleCallback(Handler.java:733)
                                                                at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                at android.os.Looper.loop(Looper.java:136)
                                                                at android.app.ActivityThread.main(ActivityThread.java:5001)
                                                                at java.lang.reflect.Method.invokeNative(Native Method)
                                                                at java.lang.reflect.Method.invoke(Method.java:515)
                                                                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
                                                                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
                                                                at dalvik.system.NativeStart.main(Native Method)