Gradle sync failed: Cause: java.lang.NullPointerException

問題引入

部分專案從alpha版本匯入到beta版本的時候會觸發以上異常，無論是rebuild亦或者gradle sync都沒有效果，依然爆出錯誤；重新開啟專案，匯入專案都無法解決。

詳細錯誤：

Error:Cause: java.lang.NullPointerException
    at sun.nio.fs.UnixPath.normalizeAndCheck(UnixPath.java:77)
    at sun.nio.fs.UnixPath.<init>(UnixPath.java
 
:71)
    at sun.nio.fs.UnixFileSystem.getPath(UnixFileSystem.java:281)
    at java.nio.file.Paths.get(Paths.java:84)
    at com.android.build.gradle.internal.scope.BuildOutput.getOutputPath(BuildOutput.java:222)
    at com.android.build.gradle.internal.scope.BuildOutputs.lambda$load$2(BuildOutputs.java
 
:243)
    at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
    at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1376)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto
 
(AbstractPipeline.java:471)
    at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
    at com.android.build.gradle.internal.scope.BuildOutputs.load(BuildOutputs.java:245)
    at com.android.build.gradle.internal.scope.BuildOutputs.load(BuildOutputs.java:184)
    at com.android.build.gradle.internal.scope.BuildOutputs.load(BuildOutputs.java:140)
    at com.android.build.gradle.internal.ide.BuildOutputsSupplier.lambda$get$1(BuildOutputsSupplier.java:55)
    at com.google.common.collect.ImmutableList.forEach(ImmutableList.java:397)
    at com.android.build.gradle.internal.ide.BuildOutputsSupplier.get(BuildOutputsSupplier.java:50)
    at com.android.build.gradle.internal.ide.BuildOutputsSupplier.get(BuildOutputsSupplier.java:35)
    at com.android.build.gradle.internal.ide.AndroidArtifactImpl.getOutputs(AndroidArtifactImpl.java:134)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.gradle.tooling.internal.adapter.ProtocolToModelAdapter$ReflectionMethodInvoker.invoke(ProtocolToModelAdapter.java:592)
    at org.gradle.tooling.internal.adapter.ProtocolToModelAdapter$AdaptingMethodInvoker.invoke(ProtocolToModelAdapter.java:397)
    at org.gradle.tooling.internal.adapter.ProtocolToModelAdapter$PropertyCachingMethodInvoker.invoke(ProtocolToModelAdapter.java:625)
    at org.gradle.tooling.internal.adapter.ProtocolToModelAdapter$SafeMethodInvoker.invoke(ProtocolToModelAdapter.java:647)
    at org.gradle.tooling.internal.adapter.ProtocolToModelAdapter$SupportedPropertyInvoker.invoke(ProtocolToModelAdapter.java:670)
    at org.gradle.tooling.internal.adapter.ProtocolToModelAdapter$InvocationHandlerImpl.invoke(ProtocolToModelAdapter.java:356)
    at com.sun.proxy.$Proxy144.getOutputs(Unknown Source)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeAndroidArtifactImpl.<init>(IdeAndroidArtifactImpl.java:57)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeVariantImpl.lambda$new$0(IdeVariantImpl.java:60)
    at com.android.tools.idea.gradle.project.model.ide.android.ModelCache.lambda$computeIfAbsent$0(ModelCache.java:31)
    at java.util.HashMap.computeIfAbsent(HashMap.java:1126)
    at com.android.tools.idea.gradle.project.model.ide.android.ModelCache.computeIfAbsent(ModelCache.java:31)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeVariantImpl.<init>(IdeVariantImpl.java:59)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeAndroidProjectImpl.lambda$new$4(IdeAndroidProjectImpl.java:88)
    at com.android.tools.idea.gradle.project.model.ide.android.ModelCache.lambda$computeIfAbsent$0(ModelCache.java:31)
    at java.util.HashMap.computeIfAbsent(HashMap.java:1126)
    at com.android.tools.idea.gradle.project.model.ide.android.ModelCache.computeIfAbsent(ModelCache.java:31)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeModel.copy(IdeModel.java:74)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeAndroidProjectImpl.<init>(IdeAndroidProjectImpl.java:87)
    at com.android.tools.idea.gradle.project.model.ide.android.IdeAndroidProjectImpl.<init>(IdeAndroidProjectImpl.java:68)
    at com.android.tools.idea.gradle.project.model.AndroidModuleModel.<init>(AndroidModuleModel.java:131)
    at com.android.tools.idea.gradle.project.sync.idea.AndroidGradleProjectResolver.populateModuleContentRoots(AndroidGradleProjectResolver.java:214)
    at org.jetbrains.plugins.gradle.service.project.AbstractProjectResolverExtension.populateModuleContentRoots(AbstractProjectResolverExtension.java:103)
    at org.jetbrains.plugins.gradle.service.project.GradleProjectResolver.doResolveProjectInfo(GradleProjectResolver.java:366)
    at org.jetbrains.plugins.gradle.service.project.GradleProjectResolver.access$200(GradleProjectResolver.java:79)
    at org.jetbrains.plugins.gradle.service.project.GradleProjectResolver$ProjectConnectionDataNodeFunction.fun(GradleProjectResolver.java:902)
    at org.jetbrains.plugins.gradle.service.project.GradleProjectResolver$ProjectConnectionDataNodeFunction.fun(GradleProjectResolver.java:886)
    at org.jetbrains.plugins.gradle.service.execution.GradleExecutionHelper.execute(GradleExecutionHelper.java:218)
    at org.jetbrains.plugins.gradle.service.project.GradleProjectResolver.resolveProjectInfo(GradleProjectResolver.java:139)
    at org.jetbrains.plugins.gradle.service.project.GradleProjectResolver.resolveProjectInfo(GradleProjectResolver.java:79)
    at com.intellij.openapi.externalSystem.service.remote.RemoteExternalSystemProjectResolverImpl.lambda$resolveProjectInfo$0(RemoteExternalSystemProjectResolverImpl.java:37)
    at com.intellij.openapi.externalSystem.service.remote.AbstractRemoteExternalSystemService.execute(AbstractRemoteExternalSystemService.java:59)
    at com.intellij.openapi.externalSystem.service.remote.RemoteExternalSystemProjectResolverImpl.resolveProjectInfo(RemoteExternalSystemProjectResolverImpl.java:37)
    at com.intellij.openapi.externalSystem.service.remote.wrapper.ExternalSystemProjectResolverWrapper.resolveProjectInfo(ExternalSystemProjectResolverWrapper.java:45)
    at com.intellij.openapi.externalSystem.service.internal.ExternalSystemResolveProjectTask.doExecute(ExternalSystemResolveProjectTask.java:66)
    at com.intellij.openapi.externalSystem.service.internal.AbstractExternalSystemTask.execute(AbstractExternalSystemTask.java:139)
    at com.intellij.openapi.externalSystem.service.internal.AbstractExternalSystemTask.execute(AbstractExternalSystemTask.java:125)
    at com.intellij.openapi.externalSystem.util.ExternalSystemUtil$3.execute(ExternalSystemUtil.java:388)
    at com.intellij.openapi.externalSystem.util.ExternalSystemUtil$5.run(ExternalSystemUtil.java:445)
    at com.intellij.openapi.progress.impl.CoreProgressManager$TaskRunnable.run(CoreProgressManager.java:726)
    at com.intellij.openapi.progress.impl.CoreProgressManager.lambda$runProcess$1(CoreProgressManager.java:176)
    at com.intellij.openapi.progress.impl.CoreProgressManager.registerIndicatorAndRun(CoreProgressManager.java:556)
    at com.intellij.openapi.progress.impl.CoreProgressManager.executeProcessUnderProgress(CoreProgressManager.java:501)
    at com.intellij.openapi.progress.impl.ProgressManagerImpl.executeProcessUnderProgress(ProgressManagerImpl.java:66)
    at com.intellij.openapi.progress.impl.CoreProgressManager.runProcess(CoreProgressManager.java:163)
    at com.intellij.openapi.progress.impl.ProgressManagerImpl$1.run(ProgressManagerImpl.java:137)
    at com.intellij.openapi.application.impl.ApplicationImpl$2.run(ApplicationImpl.java:334)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    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)

我們點選Message視窗將會看見：

解決方案

其實這個問題，並不是你的問題，而是build快取引起的問題。要解決問題需要如下幾步。

確定配置正確

根目錄確保build檔案中的版本是最新的版本；一般是當前AS對應的版本。

進入資料夾：./gradle/wrapper/ 開啟檔案：“gradle-wrapper.properties“ 確保其中對應的gradle版本為最新。

清理build

刪除你專案根目錄的 build 資料夾，以及刪除所有的module下面的 build 資料夾。

注意：是所有！！！！

同步

選擇gradle的sync操作；此時你會發現輕易就完成了同步操作。
之後你就可以rebuild專案，進行正常開發了。

END

問題本身並不複雜，解決方案也很簡單，但是不知道的朋友碰到了或許會手忙腳亂；希望能夠幫助需要的同學。