Unable to resolve error in Qualtrics Initialization

I'm a newbie in Android development and Qualtrics Integration. I'm getting an error when I'm trying to initialize an instance of Qualtrics. I have created the intercept ID and Creative ID for the Qualtrics survey that I'm using here. Here's the code for MainActivity.java:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

Qualtrics.instance().initialize("abc", "ZN_XXXXXXUZF", "SI_XXXXXXXEFO",this);

FloatingActionButton fab = (FloatingActionButton)findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Qualtrics.instance().evaluateTargetingLogic(new MyCallBack());
}
});
}
This is the error I keep getting in the logcat:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.qualtrics_apptest, PID: 6690
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.qualtrics_apptest/com.example.qualtrics_apptest.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at java.lang.StringBuilder.(StringBuilder.java:113)
at com.qualtrics.digital.SiteInterceptService.postErrorLog(SiteInterceptService.java:93)
at com.qualtrics.digital.CrashReporter.logCrash(CrashReporter.java:6)
at com.qualtrics.digital.Qualtrics.initialize(Qualtrics.java:106)
at com.qualtrics.digital.Qualtrics.initialize(Qualtrics.java:58)
at com.example.qualtrics_apptest.MainActivity.onCreate(MainActivity.java:26)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
Does anyone have any idea why this error is occurring?