NPE with QueryDSL configuration - SpringBoot < 2.3.2

[Marx2]

When trying to open swagger-ui, bug happens.
Field with the name "denyList" is read as a null here:
Field field = FieldUtils.getDeclaredField(instance.getClass(),fieldName,true);
I have no "denyList" configured anywhere, so it seems like something static in springdoc
As there's no null check, NPE is thrown.

java.lang.NullPointerException: null
	at org.springdoc.data.rest.customisers.QuerydslPredicateOperationCustomizer.getFieldValues(QuerydslPredicateOperationCustomizer.java:158) ~[springdoc-openapi-data-rest-1.4.6.jar:1.4.6]
	at org.springdoc.data.rest.customisers.QuerydslPredicateOperationCustomizer.customize(QuerydslPredicateOperationCustomizer.java:110) ~[springdoc-openapi-data-rest-1.4.6.jar:1.4.6]
	at org.springdoc.api.AbstractOpenApiResource.lambda$null$19(AbstractOpenApiResource.java:641) ~[springdoc-openapi-common-1.4.6.jar:1.4.6]

To Reproduce
Steps to reproduce the behavior:

• Spring Boot 2.2.4
• What modules and versions of springdoc-openapi are you using?
  springdoc-openapi-data-rest
  springdoc-openapi-ui
  springdoc-openapi-security
• What is the actual and the expected result using OpenAPI Description (yml or json)?
  currently error is shown: "Fetch error undefined /v3/api-docs"

Expected behavior

• add null check (denyList field is not mandatory), skip errors, generate configuration

Additional context
I suppose bug was introduce in #814