NullPointerException in com.sun.tools.javac.comp.Modules.checkCyclicDependencies when module missing

The NPE was reported here:
  http://mail.openjdk.java.net/pipermail/jigsaw-dev/2016-May/007997.html


java.lang.NullPointerException
at com.sun.tools.javac.comp.Modules.checkCyclicDependencies(jdk.compiler@9-ea/Modules.java:1222)
at com.sun.tools.javac.comp.Modules.access$400(jdk.compiler@9-ea/Modules.java:117)
at com.sun.tools.javac.comp.Modules$3.complete(jdk.compiler@9-ea/Modules.java:539)
at com.sun.tools.javac.code.Symbol.complete(jdk.compiler@9-ea/Symbol.java:602)
at com.sun.tools.javac.comp.Modules.computeTransitiveClosure(jdk.compiler@9-ea/Modules.java:925)
at com.sun.tools.javac.comp.Modules.allModules(jdk.compiler@9-ea/Modules.java:888)
at com.sun.tools.javac.comp.Modules.enter(jdk.compiler@9-ea/Modules.java:216)
at com.sun.tools.javac.main.JavaCompiler.initModules(jdk.compiler@9-ea/JavaCompiler.java:1020)
at com.sun.tools.javac.main.JavaCompiler.initModules(jdk.compiler@9-ea/JavaCompiler.java:1012)
at com.sun.tools.javac.main.JavaCompiler.compile(jdk.compiler@9-ea/JavaCompiler.java:906)
at com.sun.tools.javac.main.Main.compile(jdk.compiler@9-ea/Main.java:269)
at com.sun.tools.javac.main.Main.compile(jdk.compiler@9-ea/Main.java:144)
at com.sun.tools.javac.Main.compile(jdk.compiler@9-ea/Main.java:55)
at com.sun.tools.javac.Main.main(jdk.compiler@9-ea/Main.java:41)