5E SRD Question No on can Answer

[WhyteOne]

I have added the UA wizard and warlock to my usable stuffs in character creation. I found that when I add the raven queen as a patron for warlock I get an immunity to being frightened. I have tested this several times and this is where it is coming from. However there is no mention of gaining the immunity to being frightened in the raven queen material from the official UA website or in the material in HeroLab. In have tried to track down where this is coming from in the game files themselves through the editor, but I have had no success. Can you tell my where to find this in the game files using the editor or better yet why this is included in the UA for hero lab when I can’t find it anywhere in the official materials?