NPE in nullness detector

[ndbernardi]

     [java]   Exception analyzing com.monits.cbm.model.document.DocumentType using detector jp.co.worksap.oss.findbugs.jsr305.nullness.UnknownNullnessDetector
     [java]     java.lang.NullPointerException
     [java]       At jp.co.worksap.oss.findbugs.jsr305.nullness.UnknownNullnessDetector.getBoundGenericsInClassSignature(UnknownNullnessDetector.java:188)
     [java]       At jp.co.worksap.oss.findbugs.jsr305.nullness.UnknownNullnessDetector.findSuperMethods(UnknownNullnessDetector.java:219)
     [java]       At jp.co.worksap.oss.findbugs.jsr305.nullness.UnknownNullnessDetector.findSuperMethods(UnknownNullnessDetector.java:230)
     [java]       At jp.co.worksap.oss.findbugs.jsr305.nullness.UnknownNullnessDetector.findSuperMethods(UnknownNullnessDetector.java:157)
     [java]       At jp.co.worksap.oss.findbugs.jsr305.nullness.UnknownNullnessDetector.visit(UnknownNullnessDetector.java:75)
     [java]       At edu.umd.cs.findbugs.visitclass.BetterVisitor.visitMethod(BetterVisitor.java:351)
     [java]       At org.apache.bcel.classfile.Method.accept(Method.java:106)
     [java]       At edu.umd.cs.findbugs.visitclass.PreorderVisitor.doVisitMethod(PreorderVisitor.java:304)
     [java]       At edu.umd.cs.findbugs.visitclass.PreorderVisitor.visitJavaClass(PreorderVisitor.java:395)
     [java]       At org.apache.bcel.classfile.JavaClass.accept(JavaClass.java:215)
     [java]       At edu.umd.cs.findbugs.BytecodeScanningDetector.visitClassContext(BytecodeScanningDetector.java:38)
     [java]       At edu.umd.cs.findbugs.DetectorToDetector2Adapter.visitClass(DetectorToDetector2Adapter.java:76)
     [java]       At edu.umd.cs.findbugs.FindBugs2.analyzeApplication(FindBugs2.java:1089)
     [java]       At edu.umd.cs.findbugs.FindBugs2.execute(FindBugs2.java:283)
     [java]       At edu.umd.cs.findbugs.FindBugs.runMain(FindBugs.java:402)
     [java]       At edu.umd.cs.findbugs.FindBugs2.main(FindBugs2.java:1200)

Where DocumentType is

/*
 * Copyright (c) 2010-2014 Monits S.A. <http://www.monits.com/>
 */
package com.monits.cbm.model.document;

/**
 * Enum for Monits Document Types
 *
 * @author rpereyra
 */
public enum DocumentType {
    PROCESS, CULTURE, AVAILABLE_DEVICES,
    EQUIPEMENT_REQUEST, SUPPORT_REQUEST,
    DEVICE_REQUEST, MANAGEMENT_ORDERS;
}