Build failure on MacOS

I have java 12.0.1. I followed the instructions for installation, and upon running `./gradlew clean buildPlugin`, I got the following error:

```
> Task :buildSearchableOptions
Starting searchable options index builder
Searchable options index builder failed
java.lang.IllegalArgumentException: Argument for @NotNull parameter 'defaultValue' of com/intellij/util/ObjectUtils.notNull must not be null
at com.intellij.util.ObjectUtils.$$$reportNull$$$0(ObjectUtils.java)
at com.intellij.util.ObjectUtils.notNull(ObjectUtils.java)
at com.intellij.util.ObjectUtils.notNull(ObjectUtils.java:128)
at com.intellij.ide.ui.search.TraverseUIStarter.processKeymap(TraverseUIStarter.java:249)
at com.intellij.ide.ui.search.TraverseUIStarter.startup(TraverseUIStarter.java:123)
at com.intellij.ide.ui.search.TraverseUIStarter.main(TraverseUIStarter.java:87)
at com.intellij.idea.IdeaApplication.lambda$run$1(IdeaApplication.java:211)
at com.intellij.openapi.application.TransactionGuardImpl.performUserActivity(TransactionGuardImpl.java:195)
at com.intellij.idea.IdeaApplication.run(IdeaApplication.java:211)
at com.intellij.idea.IdeaApplication.lambda$initApplication$0(IdeaApplication.java:74)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:764)
at java.awt.EventQueue.access$500(EventQueue.java:98)
at java.awt.EventQueue$3.run(EventQueue.java:715)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:734)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:347)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
```