Uploading pdf file crashes the emulator

Question

I'm trying to upload a pdf file to the server in my android app with java.
Using the emulator, the app keeps crashing when I try to upload the file

The error I get:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.lastIndexOf(java.lang.String)' on a null object reference at com.example.parttimejob.ApplicantRegisterActivity.onActivityResult(ApplicantRegisterActivity.java:202)

Here's what happens:

After the android user presses a button to choose a pdf,a setOnClickListener activates, here is the code:

button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setType("application/pdf");
                intent.setAction(Intent.ACTION_GET_CONTENT);
                startActivityForResult(Intent.createChooser(intent, "Select PDF : "), 1);
            }
        });

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == 1 && resultCode == RESULT_OK) {
            Uri selectedFileUri = data.getData();   // get the file uri
            filePath = getPath(selectedFileUri);    // get the path of the uri
            file_name = filePath.substring(filePath.lastIndexOf("/") + 1);  // get the name of the file

            aController.setFilename(file_name);
            aController.setFilepath(filePath);

        }
    }


    public String getPath(Uri uri) {
        String[] projection = {MediaStore.Images.Media.DATA};
        Cursor cursor = managedQuery(uri, projection, null, null, null);
        int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
        cursor.moveToFirst();
        return cursor.getString(column_index);
    }

I suspect the file path to be the problem, filePath = getPath(selectedFileUri);

What's wrong with the code though?