fix!: support parsing empty tile terrain values

[devoncarew]

Description

• adjust the parsing of the Tile.terrain list to support empty terrain values
• fix FormatException when parsing a tmx file #60

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Related Issues

• FormatException when parsing a tmx file #60

[kurtome]

LGTM, but I think title should be "fix!" since it's a breaking change

[devoncarew]

LGTM, but I think title should be "fix!" since it's a breaking change

Ah, because of the type change from Tile List<int> terrain to List<int?> terrain? I suppose that would be - people using that API would see CI failures until they updated to handle nullable elements. I'll update the PR title and checkboxes. I'm not sure about the process wrt updating the changelog and pubspec versions.

[kurtome]

I'm not sure about the process wrt updating the changelog and pubspec versions.

melos will do that automatically next time we cut a release based on the PR titles. We decided recently to try to get all the breaking changes in now before we get to v1.0, so it's good timing 👍