Minor improvement in utils.py

[rainyman2012]

When we pass an empty string it's good to handle the exception. Users can handle the empty input when the program raises an exception. by the way, it's a common input and we can handle it on behalf of them.

[majiidd]

Thank you Ehsan jaan for your consideration. In most cases, input/data validation is performed by upper layers, and this if just adds more overhead. Due to the nature of the language, it's better to check data types, not values.