I would like to disable this pop-up helper thing on my editor. How do I do that? There is a weird "next" thing beside my null. Thanks.
Well, that text is called Inlay hints or Inline hints. More specifically inline parameter hints.
In the case of Java it will be the same as the parameter 'name' specified in Javadocs for the given function.
You are seeing this most likely because you have one of Inline Parameters plugins installed and enabled.
You need to go to the settings -> Search inline -> Extensions - Java -> And set the value to disabled/none.
Alternatively, you can also disable the inline extension, or uncheck the Java language from the installed extension, like below,
Once disabled your code should appear without inline parameter hints.