Kolab notes app crashes after drawing a couple of drawings in a note/book

Project Information: https://github.com/konradrenner/kolabnotes-android

Project Name : Kolab Notes

Expected behavior :

After creating a note in the Kolab notes app in a particular way, the app was expected to open the note after saving it. The particular way which I'm talking about is explained as:
When I give the name to the note and then draw something by pressing the drawing option and save the drawing and when I add another drawing to it and save the note. After saving the note and then when I try to open the note the app is expected to open the note/book.

Actual behavior :

When I follow the above mentioned procedure of making a drawing and saving it and then adding another drawing to the note and then saving it. After saving the note/book, when we click on the note/book to open it, the app crashes.

How to reproduce:

• Install the app, Kolab notes, to your phone from Fdroid.

• Open the app and click on the pencil icon to start creating a note/book.

• Write the name and summary in the first two boxes.

• Press the white screen for more options.

• Click on the drawing option to draw your drawing.

• Now press the tick icon to save your drawing.

• To draw another drawing in your note, press the screen again to get the drawing option.

• Now after completing the drawing save it and save the note.

• Now try to open the note you just created.

• The app will crash.

• Android 7.0
• App version 3.1.3

Proof of work done: https://github.com/konradrenner/kolabnotes-android/issues/181

https://github.com/syedubair

Recording of the bug: