AsSuperVisitor: type is not an erased subtype of supertype.

[cushon]

import java.io.IOException;
import java.io.Serializable;
import org.checkerframework.checker.nullness.qual.Nullable;

class T {

  public static class A implements Serializable {}

  static class G {
    public <T extends Serializable> @Nullable T g(Class<? super T> e) throws IOException {
      throw new AssertionError();
    }
  }

  static <T extends A> T f(Class<? super T> x, G y) {
    A z;
    try {
      z = y.g(x);
    } catch (IOException e) {
      throw new IllegalStateException(e);
    }
    return (T) z;
  }
}

$ ./checker-framework-3.42.0/checker/bin/javac -processor nullness T.java   |& less
error: AsSuperVisitor: type is not an erased subtype of supertype.
  type: Object
  superType: A
  ; The Checker Framework crashed.  Please report the crash.  Version: Checker Framework 3.42.0.
  Compilation unit: T.java
  Last visited tree at line 18 column 7:
        z = y.g(x);
  Exception: java.lang.Throwable; java.lang.Throwable
        at org.checkerframework.javacutil.BugInCF.<init>(BugInCF.java:34)
        at org.checkerframework.framework.type.AsSuperVisitor.errorTypeNotErasedSubtypeOfSuperType(AsSuperVisitor.java:148)
        at org.checkerframework.framework.type.AsSuperVisitor.visitDeclared_Declared(AsSuperVisitor.java:338)
        at org.checkerframework.framework.type.AsSuperVisitor.visitDeclared_Declared(AsSuperVisitor.java:30)
        at org.checkerframework.framework.util.AtmCombo.accept(AtmCombo.java:312)
        at org.checkerframework.framework.type.visitor.AbstractAtmComboVisitor.visit(AbstractAtmComboVisitor.java:34)
        at org.checkerframework.framework.type.AsSuperVisitor.visit(AsSuperVisitor.java:107)
        at org.checkerframework.framework.type.AsSuperVisitor.asSuper(AsSuperVisitor.java:88)
        at org.checkerframework.framework.util.AnnotatedTypes.asSuper(AnnotatedTypes.java:117)

[smillst]

This passes in master. I've added the test case: #6394.