Resolving Schema for system enums fails if enumsAsRef is enabled

[mdjimy]

If ModelResolver.enumsAsRef is set to true and model contains property with java.time.DayOfWeek enum, then generation of OpenAPI specification for such a model will result in the following exception:

java.lang.NullPointerException: null
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at java.base/java.util.TreeMap.put(TreeMap.java:809)
	at java.base/java.util.TreeMap.put(TreeMap.java:534)
	at io.swagger.v3.core.converter.ModelConverterContextImpl.defineModel(ModelConverterContextImpl.java:60)
	at io.swagger.v3.core.jackson.ModelResolver.resolve(ModelResolver.java:350)
	at org.springdoc.core.converters.AdditionalModelsConverter.resolve(AdditionalModelsConverter.java:155)
	at org.springdoc.core.converters.FileSupportConverter.resolve(FileSupportConverter.java:69)
	at org.springdoc.core.converters.ResponseSupportConverter.resolve(ResponseSupportConverter.java:79)
	at ...

I believe the problem is that ModelResolver.resolve( ) checks if type is not system type (using ReflectionUtils.isSystemType(type)) and if so, default value of property schema name is not inferred from its type name.

Proposed solution is to skip system type check for enum types.

Here you can find gist with minimal code example to reproduce the problem:
https://gist.github.com/mdjimy/2a08b1f9f0eb26485f2794c50df7dd35

Tested with io.swagger.core.v3:swagger-core-jakarta:2.2.8