Unable to Generate GO clients when schema has enums on it

Description

When attempting to generate GO clients from a schema that uses Enums, it fails with error :

15:58:49.856 [main] INFO  i.s.c.v.g.t.AbstractTypeScriptClientCodegen - Template folder: null
15:58:49.856 [main] INFO  i.s.c.v.g.t.AbstractTypeScriptClientCodegen - Template engine: io.swagger.codegen.v3.templates.HandlebarTemplateEngine@e98770d
15:58:49.877 [Thread-0] INFO  i.s.c.v.g.t.AbstractTypeScriptClientCodegen - Template folder: null
15:58:49.878 [Thread-0] INFO  i.s.c.v.g.t.AbstractTypeScriptClientCodegen - Template engine: io.swagger.codegen.v3.templates.HandlebarTemplateEngine@53ba3063
Exception in thread "Thread-0" java.lang.RuntimeException: Could not process model 'ASchemaName'.Please make sure that your schema is correct!
	at io.swagger.codegen.v3.DefaultGenerator.generateModels(DefaultGenerator.java:391)
	at io.swagger.codegen.v3.DefaultGenerator.generate(DefaultGenerator.java:793)
	at io.swagger.codegen.v3.cli.cmd.Generate.run(Generate.java:388)
	at java.base/java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException: Cannot invoke "String.equals(Object)" because "codegenModel.dataType" is null
	at io.swagger.codegen.v3.generators.DefaultCodegenConfig.fromModel(DefaultCodegenConfig.java:1466)
	at io.swagger.codegen.v3.generators.go.AbstractGoCodegen.fromModel(AbstractGoCodegen.java:565)
	at io.swagger.codegen.v3.DefaultGenerator.processModels(DefaultGenerator.java:1068)
	at io.swagger.codegen.v3.DefaultGenerator.generateModels(DefaultGenerator.java:380)
	... 3 more

Swagger-codegen version

Whichever version is in the docker image swaggerapi/swagger-codegen-cli-v3. 3.0.59?

Swagger declaration file content or url

openapi: 3.1.0

components:
  schemas:
    ASchemaName:
      type: string
      enum: [value1,value2,value3]
   

Command line used for generation

This works
docker run --rm -v ${PWD}:/local swaggerapi/swagger-codegen-cli-v3 generate -i /local/simplest.yml -l javascript -o /local/out/go

This does not
docker run --rm -v ${PWD}:/local swaggerapi/swagger-codegen-cli-v3 generate -i /local/simplest.yml -l go -o /local/out/go

Steps to reproduce

docker run --rm -v ${PWD}:/local swaggerapi/swagger-codegen-cli-v3 generate -i /local/simplest.yml -l go -o /local/out/go

Related issues/PRs

Unknown

Suggest a fix/enhancement

Reproduce the failure with simplest.yml and the Docker generate command, then trace the reported path through DefaultCodegenConfig.fromModel and generators.go.AbstractGoCodegen.fromModel. Compare the Go and JavaScript runs and add regression coverage for the enum schema; done means Go client generation completes without the NullPointerException.