The Doclet works for large numbers of source files, but fails with below NPE when apparently unremarkable source files are included.

[javadoc] 1 error
  [javadoc] 153 warnings
  [javadoc] java.lang.NullPointerException
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap.purgeMemberLevelMap(VisibleMemberMap.java:253)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap.access$300(VisibleMemberMap.java:49)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap$ClassMembers.<init>(VisibleMemberMap.java:325)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap$ClassMembers.mapClass(VisibleMemberMap.java:350)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap$ClassMembers.mapClass(VisibleMemberMap.java:351)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap$ClassMembers.build(VisibleMemberMap.java:341)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap$ClassMembers.access$100(VisibleMemberMap.java:291)
  [javadoc] at com.sun.tools.doclets.internal.toolkit.util.VisibleMemberMap.<init>(VisibleMemberMap.java:127)
  [javadoc] at ...