fix: Do not create cors_configuration when variable not provided

[durnik-ivo]

Description

Filters out null values when checking for var.cors_configuration content and deletes default value for var.cors_configuration.expose_headers, which is not required.

Motivation and Context

When var.cors_configuration is not passed to the module, its content is not {}, because a type is specified for the variable:

      + cors_configuration = {
          + allow_credentials = null
          + allow_headers     = null
          + allow_methods     = null
          + allow_origins     = null
          + expose_headers    = []
          + max_age           = null
        }

this causes condition for the dynamic block to be evaluted incorrectly:

resource "aws_apigatewayv2_api" "this" {
  # [...]

  dynamic "cors_configuration" {
    for_each = local.is_http && length(var.cors_configuration) > 0 ? [var.cors_configuration] : []

    content {
      # [...]
    }
  }

and adds an empty cors_configuration section to the resource:

  # module.api_gateway_orig.aws_apigatewayv2_api.this[0] will be created
  + resource "aws_apigatewayv2_api" "this" {
      + api_endpoint                 = (known after apply)
      + api_key_selection_expression = "$request.header.x-api-key"
      + arn                          = (known after apply)
      + execution_arn                = (known after apply)
      + id                           = (known after apply)
      + name                         = "idurnik_test_module"
      + protocol_type                = "HTTP"
      + route_selection_expression   = "$request.method $request.path"
      + tags                         = {
          + "terraform-aws-modules" = "apigateway-v2"
        }
      + tags_all                     = {
          + "terraform-aws-modules" = "apigateway-v2"
        }

      + cors_configuration {} # <---- Adds empty cors section
    }

instead this section should not be configured:

  # module.api_gateway_mine.aws_apigatewayv2_api.this[0] will be created
  + resource "aws_apigatewayv2_api" "this" {
      + api_endpoint                 = (known after apply)
      + api_key_selection_expression = "$request.header.x-api-key"
      + arn                          = (known after apply)
      + execution_arn                = (known after apply)
      + id                           = (known after apply)
      + name                         = "idurnik_test_module_mine"
      + protocol_type                = "HTTP"
      + route_selection_expression   = "$request.method $request.path"
      + tags                         = {
          + "terraform-aws-modules" = "apigateway-v2"
        }
      + tags_all                     = {
          + "terraform-aws-modules" = "apigateway-v2"
        }

      # <--- no cors section
    }

Breaking Changes

Yes.

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

[yungbender]

Adding on top of this, when you propagate this

      + cors_configuration {}

Into your api gateway, it forces the gateway to start overriding your CORS headers returned from the integrations, which makes this module a hassle to use.

[bryantbiggs]

I don't think this is a valid change

[bryantbiggs]

I think this might be a valid change - will test it out

[bryantbiggs]

not valid - updated in b7ec703

[antonbabenko]

This PR is included in version 5.1.1 🎉

[github-actions]

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