Fix Accessing Object via Dictionary

[davidvonthenen]

Proposed changes

Addresses issue submitted by @leddy231 : #294

This also addresses:

• implements __str__ to provide a better print() experience
• fixes a serialization issue on empty objects which was causing an exception: if _dict["intents_info"] is not None: -> if "intents_info" in _dict:
• fix missing sentiment segments:

if "sentiment" in _dict:
    _dict["sentiment"] = Sentiment.from_dict(_dict["sentiment"])

• Some fields like speaker, speaker_confidence, etc needed to be excluded from the JSON when not set
• Did an oops where .items() should only be used on Dict[] objects (this is the reported issue)

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update or tests (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTING doc
• I have lint'ed all of my code using repo standards
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments