Javafx expression binding Cannot resolve symbol but runs fine

Hi all,

I have just encountered a weird problem with intellij idea 2018. I got an error "Cannot resolve symbol" in my expression binding in my fxml file for my javafx project. Idea marked the error code red, but when I try to run the whole application, it works without any problem. I also tried the exact same code in netbeans and it does not show any error message. I assume there are no actual error in the code, but the red error just bothers me.

I did some research online and tried the following steps try to resolve this problem:

1. File | Invalidate Caches / Restart: This solved the problem momentarily, after indexing is done, Idea once again highlighted the code red.
2. Delete the system folder \.IdeaIC2018.1: Once again after the indexing is done the error popped up.
3. Updated JDK to jdk1.8.0 _172: Error still exists.
4. Delete .idea folder and reimport the project: Error still exists.

The version I am running:

IntelliJ IDEA 2018.1.3 (Community Edition)
Build #IC-181.4892.42, built on May 8, 2018
JRE: 1.8.0_152-release-1136-b38 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0

The error I am getting:

Runs as expected without any problem:

Okay I am really out of ideas what is actually causing this and how to solve this, so any suggestion would be really appreciated!

Thanks!