Resolve "Performance optimization 2"

Closes #442 (closed)

added Interpreter Refactoring labels

added 4 commits

• 929cc67a - create value property in order to defer de-serialization
• 607be120 - include a sentence about the type: null option in the docs
• 416e2dc5 - explicitly assert datastore is not None, versions 6 and 7 compatible
• 754ccf9f - avoid unnecessary serialization calls, do some refactoring to_dict()

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marked this merge request as ready

mentioned in commit f3c2c294

merged