Gradle wrapper on Hybris 6.6 Ant

Greeting everyone,
I’m trying to create gradle wrapper on Hybris (version 6.6) ant according to this tutorial.

How to move hybris from ant to gradle tutorial

I have the next error during running ./gradlew clean build

A problem occurred evaluating root project 'platform'.
> Failed to apply plugin [class 'org.gradle.language.base.plugins.LifecycleBasePlugin']
   > Cannot add task 'clean' as a task with that name already exists.

I tried to remove tasks which are starting with clean prefixes, but it didn’t solve my issue.
Does anybody know how to fix this problem? And make hybris ant work with gradle?