Codegen Ignoring @Schema(nullable=false) annotation (JAVA) with redundant null checks.

Description

The code generated via swagger-codegen is placing a nullcheck on a non-nullable field. As this field is also required, a redundant nullcheck is being performed. 1 nullcheck for the param not being null to avoid throwing exception and another nullcheck before placing the headers in the localVarHeaderParams.

If the parameter's schema annotation is defined as "nullable=false", there shouldn't be a nullcheck on this value.

Swagger-codegen version

3.0.8

Command line used for generation

(use xml for ant build, extracted cmd line args)
generate -i https://serverhost22/api/openapi.json -c config.json -l java --library jersey2

Steps to reproduce

1. Create a String argument for a given operation.

2. Annotate as follows: See Parameter(Schema())

@Operation(summary = "Release information", tags = {SwaggerConstants.TAG_CRUISE}, description = "Executes to release",
parameters = {@Parameter(in = ParameterIn.HEADER, name = SwaggerConstants.SESSION_ID, schema = @Schema(nullable = false, required = true))},
responses = {@ApiResponse(responseCode = "200", description = "ReleaseStateroomResponse with stateroom release information.",
content = @Content(mediaType = MediaType.APPLICATION_JSON, schema = @Schema(implementation = Release.class)))}) }

3. When the code is generated, the method will look like this with a redunant nullcheck:
   

Suggest a fix/enhancement

If the param has the Schema annotation with nullable = false, don't insert a nullcheck.

I'd be happy to help but am not sure where to look in the codegen files to get a fix implemented. Let me know if this is my problem and is by design.

Reproduce the issue with swagger-codegen 3.0.8 using the provided OpenAPI annotation and the Java jersey2 generation command. Trace the generated operation method's parameter handling and verify that a parameter marked nullable=false and required=true no longer receives the redundant null check, while other parameters retain their existing behavior.