解决升级到Android Studio 3 Beta版本编译异常
Gradle sync failed: Cause: java.lang.NullPointerException
问题引入
部分项目从alpha版本导入到beta版本的时候会触发以上异常，无论是rebuild亦或者gradle sync都没有效果，依然爆出错误；重新打开项目，导入项目都无法解决。
详细错误：
Error:Cause: java.lang.NullPointerException
at sun.nio.fs.UnixPath.normalizeAndCheck(UnixPath.java:77)
at sun.nio.fs.UnixPath.(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.(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$0(ModelCache.java:31)
at java.util.HashMap.computeIfAbsent(HashMap.java:1126)
at com.android.tools.idea.gradle.project.model.ide.android.ModelCache.computeIfAbsent(ModelCache.java:31)
at com.android.tools.idea.gradle.project.model.ide.android.IdeVariantImpl.(IdeVariantImpl.java:59)
at com.android.tools.idea.gradle.project.model.ide.android.IdeAndroidProjectImpl.lambda$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.(IdeAndroidProjectImpl.java:87)
at com.android.tools.idea.gradle.project.model.ide.android.IdeAndroidProjectImpl.(IdeAndroidProjectImpl.java:68)
at com.android.tools.idea.gradle.project.model.AndroidModuleModel.(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) 我们点击Message窗口将会看见：
解决方案
其实这个问题，并不是你的问题，而是build缓存引起的问题。要解决问题需要如下几步。
确定配置正确
根目录确保build文件中的版本是最新的版本；一般是当前AS对应的版本。
进入文件夹：./gradle/wrapper/ 打开文件：“gradle-wrapper.properties“ 确保其中对应的gradle版本为最新。
清理build
删除你项目根目录的 build 文件夹，以及删除所有的module下面的 build 文件夹。
注意：是所有！！！！
同步
选择gradle的sync操作；此时你会发现轻易就完成了同步操作。
之后你就可以rebuild项目，进行正常开发了。
END
问题本身并不复杂，解决方案也很简单，但是不知道的朋友碰到了或许会手忙脚乱；希望能够帮助需要的同学。