尝试从JAR读取文件时的NPE

Question

当我尝试使用以下代码读取JAR内的目录时：

getClass().getResourceAsStream('/some-dir').text

我使用以下stacktrace获得NPE：

Exception in thread "main" java.lang.NullPointerException
    at java.io.FilterInputStream.close(FilterInputStream.java:181)
    at sun.net.www.protocol.jar.JarURLConnection$JarURLInputStream.close(JarURLConnection.java:108)
    at sun.nio.cs.StreamDecoder.implClose(StreamDecoder.java:378)
    at sun.nio.cs.StreamDecoder.close(StreamDecoder.java:193)
    at java.io.InputStreamReader.close(InputStreamReader.java:199)
    at java.io.BufferedReader.close(BufferedReader.java:525)
    at org.codehaus.groovy.runtime.DefaultGroovyMethodsSupport.closeWithWarning(DefaultGroovyMethodsSupport.java:90)
    at org.codehaus.groovy.runtime.IOGroovyMethods.getText(IOGroovyMethods.java:892)
    at org.codehaus.groovy.runtime.IOGroovyMethods.getText(IOGroovyMethods.java:835)
    at org.codehaus.groovy.runtime.dgm$833.doMethodInvoke(Unknown Source)
    at org.codehaus.groovy.reflection.GeneratedMetaMethod$Proxy.doMethodInvoke(GeneratedMetaMethod.java:73)
    at org.codehaus.groovy.runtime.metaclass.MethodMetaProperty$GetBeanMethodMetaProperty.getProperty(MethodMetaProperty.java:76)
    at org.codehaus.groovy.runtime.callsite.GetEffectivePojoPropertySite.getProperty(GetEffectivePojoPropertySite.java:64)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGetProperty(AbstractCallSite.java:296)
    at com.blabla.Main.test(Main.groovy:68)
    at com.blabla.Main.main(Main.groovy:78)

奇怪的是，只有在执行JAR时才抛出异常。从IDE（IntelliJ IDEA）执行它时，它可以正常工作。