public static boolean isConcrete(Class<?> klass) {
        int mod = klass.getModifiers();
        return !Modifier.isAbstract(mod) && !Modifier.isInterface(mod);
    }
Verify the given class corresponds to a concrete class and not to an abstract class or
interface.
@param klass the class object.
@return true if the argument is a concrete class, false if it's abstract or interface.
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/isolation/PluginUtils.java