Findbugs Gradle插件失败

我试图在gradle中使用findbugs插件，但它不起作用。下面是片段gradle配置

apply plugin: 'findbugs'

dependencies {
    findbugsPlugins fileTree(dir: "$toolsHome/findbugs", include: '*.jar')
}

findbugs {
    toolVersion = "3.0.1"
    sourceSets = [sourceSets.main]
    ignoreFailures = true
    reportsDir = file("$project.buildDir/findbugsReports")
    effort = "max"
    reportLevel = "low"
    excludeBugsFilter = file(toolsHome + File.separator + "findbugs" + File.separator + "findbugs-exclude.xml")
}

堆栈跟踪：

有人能指点我我的配置有什么问题吗