FULL PRODUCT VERSION :
java version "1.8.0"
Java(TM) SE Runtime Environment (build 1.8.0-b132)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode)

and

java 9-ea
Java(TM) SE Runtime Environment (build 9-ea+152-jigsaw-nightly-h5986-20170119)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+152-jigsaw-nightly-h5986-20170119, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 10.0.14393]

A DESCRIPTION OF THE PROBLEM :
Issue originally reported at https://issues.apache.org/jira/browse/MJAVADOC-478

Javadoc contains a link to the simple name of a class (Requirements)

I assume NPE is caused because Requirements cannot be resolved.

REGRESSION. Last worked in version 7u76

ADDITIONAL REGRESSION INFORMATION:
java version "1.7.0_55"
Java(TM) SE Runtime Environment (build 1.7.0_55-b13)
Java HotSpot(TM) 64-Bit Server VM (build 24.55-b03, mixed mode)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
https://issues.apache.org/jira/browse/MJAVADOC-478 contains an attachement

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
a clear javadoc error message (not caused by a NPE)
ACTUAL -
java.lang.NullPointerException

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Java8 only gives java.lang.NullPointerException

Java9 comes with the following stacktrace
java.lang.NullPointerException
        at jdk.compiler/com.sun.tools.javac.comp.Enter.getClassEnv(Enter.java:159)
        at jdk.compiler/com.sun.tools.javac.api.JavacTrees.getAttrContext(JavacTrees.java:885)
        at jdk.compiler/com.sun.tools.javac.api.JavacTrees.attributeDocReference(JavacTrees.java:422)
        at jdk.compiler/com.sun.tools.javac.api.JavacTrees.getElement(JavacTrees.java:407)
        at jdk.compiler/com.sun.tools.doclint.Checker.visitReference(Checker.java:849)
        at jdk.compiler/com.sun.tools.doclint.Checker.visitReference(Checker.java:102)
        at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCReference.accept(DCTree.java:631)
        at jdk.compiler/com.sun.source.util.DocTreePathScanner.scan(DocTreePathScanner.java:71)
        at jdk.compiler/com.sun.source.util.DocTreeScanner.visitLink(DocTreeScanner.java:296)
        at jdk.compiler/com.sun.tools.doclint.Checker.visitLink(Checker.java:763)
        at jdk.compiler/com.sun.tools.doclint.Checker.visitLink(Checker.java:102)
        at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCLink.accept(DCTree.java:500)
        at jdk.compiler/com.sun.source.util.DocTreePathScanner.scan(DocTreePathScanner.java:71)
        at jdk.compiler/com.sun.source.util.DocTreeScanner.scanAndReduce(DocTreeScanner.java:83)
        at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:98)
        at jdk.compiler/com.sun.source.util.DocTreeScanner.scanAndReduce(DocTreeScanner.java:106)
        at jdk.compiler/com.sun.source.util.DocTreeScanner.visitDocComment(DocTreeScanner.java:184)
        at jdk.compiler/com.sun.tools.doclint.Checker.visitDocComment(Checker.java:231)
        at jdk.compiler/com.sun.tools.doclint.Checker.visitDocComment(Checker.java:102)
        at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCDocComment.accept(DCTree.java:132)
        at jdk.compiler/com.sun.source.util.DocTreePathScanner.scan(DocTreePathScanner.java:50)
        at jdk.compiler/com.sun.tools.doclint.Checker.scan(Checker.java:193)
        at jdk.compiler/com.sun.tools.doclint.DocLint.scan(DocLint.java:348)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.WorkArounds.runDocLint(WorkArounds.java:108)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getDocCommentTree0(Utils.java:3028)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getDocCommentTree(Utils.java:3056)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils$WeakSoftHashMap.computeIfAbsent(Utils.java:3238)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getCommentHelper(Utils.java:2871)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.hasBlockTag(Utils.java:2953)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.hasBlockTag(Utils.java:2949)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.isHidden(Utils.java:1553)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.ClassTree.buildTree(ClassTree.java:177)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.ClassTree.<init>(ClassTree.java:120)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.startGeneration(AbstractDoclet.java:200)
        at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.run(AbstractDoclet.java:115)
        at jdk.javadoc/jdk.javadoc.doclets.StandardDoclet.run(StandardDoclet.java:71)
        at jdk.javadoc/jdk.javadoc.internal.tool.Start.parseAndExecute(Start.java:604)
        at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:424)
        at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:341)
        at jdk.javadoc/jdk.javadoc.internal.tool.Main.execute(Main.java:63)
        at jdk.javadoc/jdk.javadoc.internal.tool.Main.main(Main.java:52)
1 error

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package org.bitbucket.cowwoc.requirements.guava;

/**
 * The following link tag causes a NullPointerException: {@link Requirements}.
 */
public interface GuavaVerifiers {
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use FQN(?)