HIGH PRIO - Fix missing storage key vulnerability

[TheMineWay]

When you read a key that does not exists it raises an error that might clear ALL data from the storage.

Fix 1:

• Before reading, check if the key is present.
• If is not present, run fallback code if present.
• Do not raise an error that can clear data.

Fix 2:

• When an error is thrown, check if the key was present.
• If it was not present, do not run data clear code.