
replace code 
```java
  ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
    if (loader == null) {
        EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
        loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
    }
  return loader;
```

to

```java
return (ExtensionLoader<T>) EXTENSION_LOADERS.computeIfAbsent(type, k -> new ExtensionLoader<T>(type));
```


* @param clazz extension class
     * @throws IllegalStateException when extension with the same name has already been registered.
     */
    public void addExtension(String name, Class<?> clazz) {
        getExtensionClasses(); 
        if (!type.isAssignableFrom(clazz)) {
            throw new IllegalStateException("Input type " +
                    clazz + " doesn't implement the Extension " + type);
        }
        if (clazz.isInterface()) {
            throw new IllegalStateException("Input type " +
                    clazz + " can't be interface!");
        }
        if (!clazz.isAnnotationPresent(Adaptive.class)) {
            if (StringUtils.isBlank(name)) {
                throw new IllegalStateException("Extension name is blank (Extension " + type + ")!");
            }
            if (cachedClasses.get().containsKey(name)) {
                throw new IllegalStateException("Extension name " +
                        name + " already exists (Extension " + type + ")!");
            }
            cachedNames.put(clazz, name);
            cachedClasses.get().put(name, clazz);
        } else {
            if (cachedAdaptiveClass != null) {
                throw new IllegalStateException("Adaptive Extension already exists (Extension " + type + ")!");
            }
            cachedAdaptiveClass = clazz;
        }
    }