Optional Enum Input Parameter is Invalidated in the Compiler Plugin.

[ThisaruGuruge]

Description:
For the GraphQL resources, we can have string, int, boolean, float, or enum as input parameters. It should be valid to have any of these parameter type unionized with nil (Optional parameter). But currently, when an input is an optional enum, the compiler is throwing an error.

Consider the following example:

public enum Bar {
    BAZ,
    ZAB,
    DOO
}

resource function get foo(Bar? bar) returns Foo {
    // ....
}