[java] generated enum arguments lack validation

[optionsome]

Which packages are impacted by your issue?

@graphql-codegen/java

Describe the bug

Reading in arguments with generated types crashes due to enum arguments lacking null validation.

Your Example Website or App

https://stackblitz.com/edit/github-val3pw

Steps to Reproduce the Bug or Issue

1. Create an input type with with an enum field and some other field(s)
2. Generate types for the query
3. Create query where the enum field is not provided but some other fields are
4. Try creating a new instance of query arguments with the graphql-java DataFetchingEnvironment from the query

Expected behavior

Creating a new instance of query arguments should not crash if some field is not defined in the arguments provided in an incoming query.

Screenshots or Videos

No response

Platform

• OS: Linux
• NodeJS: v16.20.2
• graphql version: 16.8.1
• @graphql-codegen/java version(s): 4.0.0

Codegen Config File

No response

Additional context

The code crashes because it tries to call enum's valueOf method with a null value.

[saihaj]

released @graphql-codegen/java@4.0.1

[optionsome]

Thanks for the really fast review @saihaj !