我试图通过在我的mavenized android项目上运行ant emma来获取覆盖率报告，其他一切进展顺利，但我在运行时碰到了NullPointerException
ant emma debug install test.
输出是：
test:
[echo] WARNING: Code Coverage is currently only supported on the emulator and rooted devices.
[echo] Running tests ...
[exec]
[exec] com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp.MainActivityTest:INSTRUMENTATION_RESULT: shortMsg=java.lang.NullPointerException
[exec] INSTRUMENTATION_RESULT: longMsg=java.lang.NullPointerException: Unable to start activity ComponentInfo{com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp/com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp.MainActivity}: java.lang.NullPointerException
[exec] INSTRUMENTATION_CODE: 0
[echo] Downloading coverage file into project directory...
[exec] remote object '/data/data/com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp/coverage.ec' does not exist
我该如何调试？我想知道NPE发生在哪里。