Update models.py

[amaney]

This will fix KeyError on entry['comments']['data'] when using a sandboxed app

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[gteodoru]

when will this be merged

[deluss-c]

Looking forward to have it merged.

[rafael-h-ferreira]

The whole object_from_dictionary method relies too much on the dictionary structure. If one of those keys is not present, it raises exceptions.
Made a bigger modification regarding this issue: #237