public static <T> ExtensionLoader<T> getExtensionLoader(final Class<T> clazz, final ClassLoader cl) {
        
        Objects.requireNonNull(clazz, "extension clazz is null");
        
        if (!clazz.isInterface()) {
            throw new IllegalArgumentException("extension clazz (" + clazz + ") is not interface!");
        }
        if (!clazz.isAnnotationPresent(SPI.class)) {
            throw new IllegalArgumentException("extension clazz (" + clazz + ") without @" + SPI.class + " Annotation");
        }
        ExtensionLoader<T> extensionLoader = (ExtensionLoader<T>) LOADERS.get(clazz);
        if (Objects.nonNull(extensionLoader)) {
            return extensionLoader;
        }
        LOADERS.putIfAbsent(clazz, new ExtensionLoader<>(clazz, cl));
        return (ExtensionLoader<T>) LOADERS.get(clazz);
    }
@Test
    public void testGetExtensionLoaderIsNull() {
        try {
            ExtensionLoader.getExtensionLoader(null);
            fail();
        } catch (NullPointerException expected) {
            assertThat(expected.getMessage(), containsString("extension clazz is null"));
        }
    }