Not sure if that's a bug, but looking at JDK-8130937: what is the expected result for "C": "false" or "null"?

import java.beans.IntrospectionException;
import java.beans.Introspector;
import javax.swing.SwingContainer;

public class SwingContainerTest {
    
    @SwingContainer
    public class A {}
    
    @SwingContainer(false)
    public class B {}
    
    public class C {}
    
    static void test(Class<?> c) throws IntrospectionException {
        System.out.println(c.getSimpleName() + ": " +
                Introspector.getBeanInfo(c, Object.class).getBeanDescriptor().getValue("isContainer"));
    }
    
    public static void main(String[] args) throws IntrospectionException {
        test(A.class);
        test(B.class);
        test(C.class);
    }
}

Output (JDK9 b72, Win 7):

A: true
B: false
C: null