code: @Nullable
      public <T> Class<Provider<T>> getFactoryClass(Class<T> classDefinition) {
          //noinspection unchecked
          return (Class)factoryClasses.getRootValue().get(classDefinition);
      }
docs: Returns a factory class to instantiate a certain class.
  
  @param classDefinition the class that is to be instantiated.
  @param <T> the type of the class to be instantiated.
  
  @return a factory method for the specified class.