Kotlin script .kts support -- not recognizing "args"?

By creating a .kts file and copying the code snippet at https://kotlinlang.org/docs/tutorials/command-line.html#using-the-command-line-to-run-scripts into it, the editor marks "args" as an error but the code can be run correctly.

Did I miss some settings or it's a small bug of IDEA?

This is the version I used:

IntelliJ IDEA 2017.3.3 (Ultimate Edition)
Build #IU-173.4301.25, built on January 16, 2018
JRE: 1.8.0_152-release-1024-b11 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Mac OS X 10.13.2