Example:

doc = {"signature": "ABC", "providers": ["foo", "bar"]}

my_collection.insert_one(doc)

p doc   # => {:signature=>"ABC", :providers=>["foo", "bar"]}

Notice how the keys have been replaced by symbols.

Functions should never modify their arguments in-place unless it is explicitly documented. In this case, it's obviously a bug. I haven't tested "insert_many" but it might have the same issue.