Fix three code bugs

[tomerazran]

Fixes multiple bugs related to exception handling, type checking logic, error robustness, and code clarity.

This PR addresses four specific issues:

1. Replaces NotImplemented() with NotImplementedError() in cache.py for proper exception raising.
2. Corrects type checking order in helpers.py (bool before int, datetime before date) to prevent incorrect type identification.
3. Adds a check for empty port dictionaries in client.py to prevent IndexError.
4. Adds an explicit return None in cache.py when data decoding fails, improving code clarity.

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