Declare transaction fails when the declarations file contains an empty line

[ericnordelo]

If the file exists and contains an empty line, an exception will be raised from checking if alias exists in this line:

https://github.com/OpenZeppelin/nile/blob/0c9bf0e2c2f0035fdb3349d2603557f32d5e075f/src/nile/core/declare.py#L22

The issue occurs from trying to call normalize_number on an empty hash.