Tom Sanderson

x_Icon null safety compile warnings

1

When x_icon ^0.0.5 is included in a project, when that project is compiled (discovered during unit test execution) it throws two warnings in icon.dart: ``` /home/asdef/.pub-cache/hosted/pub.dartlang.org/x_icon-0.0.5/lib/src/icon.dart:51:24: Warning: Operand of null-aware...

11253: Update handlebars version

5

### PR checklist - [X ] Read the [contribution guidelines](https://github.com/swagger-api/swagger-codegen/blob/master/CONTRIBUTING.md). - [N/A ] Ran the shell script under `./bin/` to update Petstore sample so that CIs can verify the change....