fix(undefined data): undefined issue in normalizeData member function

[dependentmadani]

Problem:

An issue of reading undefined by toString.

Cause:

The level parameter in data object is not checked for possibility of undefined.

Solution:

Check on the level content availability in the object, so it can be converted into string.

Resolves #112

[Aryanop0914]

any update on it how can it be solved?