fix: check null method for open api

[mndeveci]

Issue #, if available:
N/A

Description of changes:
Checks if method is not None before proceeding to work on it.

Description of how you validated changes:
Adding a new test case and verifying the older ones.

Checklist:

• Add/update unit tests using:
  • Correct values
  • Bad/wrong values (None, empty, wrong type, length, etc.)
  • Intrinsic Functions
• Add/update integration tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Do these changes include any template validations?
  • Did the newly validated properties support intrinsics prior to adding the validations? (If unsure, please review Intrinsic Functions before proceeding).
    • Does the pull request ensure that intrinsics remain functional with the new validations?

Examples?

Please reach out in the comments, if you want to add an example. Examples will be
added to sam init through https://github.com/awslabs/aws-sam-cli-app-templates/

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[torresxb1]

I see this for method_definition in self.get_conditional_contents(method) is used a few times in the file. In order to catch this early without having to run this validation each time, could we add this check in the constructor?
We do something like this in the SwaggerEditor constructor: https://github.com/aws/serverless-application-model/blob/develop/samtranslator/swagger/swagger.py#L65

By the way, could we also add this check on the SwaggerEditor 🙏

[torresxb1]

oh, I was too late

[mndeveci]

oh, I was too late

No worries, let me raise a new PR to address your comment.