TldScannerでNullPointerExceptionが出て起動しない

僕は普段、開発用としてTomcat-9.0.0系を使っています。

先ほどTomcat-9.0.0-M6に更新したら、このようなエラーが出て起動しなくなりました。

java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/foobar]]
    at java.util.concurrent.FutureTask.report(FutureTask.java:122)
    at java.util.concurrent.FutureTask.get(FutureTask.java:192)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:911)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:890)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:152)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1403)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1393)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/foobar]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:158)
    ... 6 more
Caused by: java.lang.NullPointerException
    at org.apache.jasper.servlet.TldScanner$TldScannerCallback.scanWebInfClasses(TldScanner.java:395)
    at org.apache.tomcat.util.scan.StandardJarScanner.scan(StandardJarScanner.java:208)
    at org.apache.jasper.servlet.TldScanner.scanJars(TldScanner.java:262)
    at org.apache.jasper.servlet.TldScanner.scan(TldScanner.java:104)
    at org.apache.jasper.servlet.JasperInitializer.onStartup(JasperInitializer.java:103)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5183)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:152)
    ... 6 more

該当箇所のソースは以下の通り。

@Override
public void scanWebInfClasses() throws IOException {
    // This is used when scanAllDirectories is enabled and one or more
    // JARs have been unpacked into WEB-INF/classes as happens with some
    // IDEs.

    Set<String> paths = context.getResourcePaths(WEB_INF + "classes/META-INF");

    for (String path : paths) { // ← 395行目
        if (path.endsWith(TLD_EXT)) {
            try {
                parseTld(path);
            } catch (SAXException e) {
                throw new IOException(e);
            }
        }
    }
}

見ての通り、pathsがnullです。

なぜだ…？と思って当該アプリケーションのMETA-INFを見てみると、空ディレクトリでした。もしやと思い、META-INFを消すと元通りに起動するようになりました。まぁ軽いバグの一種なんですかね。

ちなみに、この現象は8.5.2でも起きるようです。（該当箇所のソースが同一なので）