Null Observer Exception

[gabriel-vanca]

NullRef exception is thrown in Reset() upon pressing the Clear button.

This PR adds a NULL check verification and cleans up the file a bit.

⚠️ However, while this PR fixes the crash, further investigation is required to determine what causes the Null element to be added. Maybe a JSON parsing error when reading the file from the cache?

See #160

[coenm]

Thanks.