Platforms affected

iOs

Motivation and Context

I think it should fix #108

Description

Just replace nil values with empty string since NSDictionary crashes in that case

Testing

Don't sure how to test it, since it's pretty rare case.

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary