How to set up Community Edition with Zulu OpenJDK 11?

I have to change from Oracle JDK 8 to Zulu OpenJDK 11, and I can't seem to get InteliJ to recognize the standard class packages.  I pointed it to the Zulu SDK, but IJ doesn't recognize basic classes like String and IOException.  Oddly it does recognize more specialized classes like the javax.servlet package, but it doesn't know java.io or java.util.  I'm guessing this has something to do with the Java module feature introduced in Java 9?  But I can't find any reference to this kind of problem.  (Lots of folks having trouble with JavaFX, I think that's a separate issue.)  Anyone see this before?