private void appendInjectable(String key, Injectable<?> clazz, boolean overwrite) {
        final List<Injectable<?>> list = Optional.ofNullable(
            injectables.remove(key)
        ).orElseGet(LinkedList::new);

        if (overwrite) {
            list.clear();
        }

        list.add(clazz);
        injectables.put(key, list);
    }
Default implementation of the {@link InjectorBuilder}-interface.

@author Emil Forslund
@since  1.2.0
common-parent/injector/src/main/java/com/speedment/common/injector/internal/InjectorBuilderImpl.java