* wrap sdk callsite in try/catch to handle error appropriately
`encryptService.decryptString()` calls code in the internal SDK which when provided an invalid
key returns `CryptoError::InvalidMac`. The originating callsite has been wrapped in a try/catch
in order to intercept the error and return false so that logic in parse() may return
a more appropriate error message in the UI.
* add unit test and explanatory comment
* remove misleading comment
* remove null comparison and unused variable
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