How can i create new permission and add that in

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Hello,

How can i add new permission and add on add

I am using the following mode, it is creating permission but not adding it 

Innovator inn = this.getInnovator();
string docid = this.getProperty("id","");
Item permissions = this.newItem("Permission", "add");
permissions.setProperty("name", docid);
permissions = permissions.apply();
this.setProperty("permission_id", permissions.getID());   
	return this;