[JENKINS-60816] Missing null check when traversing type hierarchy of interfaces

core/src/main/java/hudson/ExtensionFinder.java

@@ -497,7 +497,7 @@ public abstract class ExtensionFinder implements ExtensionPoint {
                         m.setAccessible(true);
                         m.invoke(ecl, c);
                     }
-                    for (Class cc = c; cc != Object.class; cc = cc.getSuperclass()) {
+                    for (Class<?> cc = c; cc != Object.class && cc != null; cc = cc.getSuperclass()) {
                         /**
                          * See {@link com.google.inject.spi.InjectionPoint#getInjectionPoints(TypeLiteral, boolean, Errors)}
                          */