问题
Android Stuido 3.0 alpha 升级到 Android Studio 3.0 beta，gradle 同步之前的项目错误：
Gradle sync failed: Cause: java.lang.NullPointerException
at sun.nio.fs.WindowsPathParser.parse(WindowsPathParser.java:98)
at sun.nio.fs.WindowsPathParser.parse(WindowsPathParser.java:77)
at sun.nio.fs.WindowsPath.parse(WindowsPath.java:94)
at sun.nio.fs.WindowsFileSystem.getPath(WindowsFileSystem.java:255)
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)
解决方法
有两种方式：命令行方式和IDE交互方式
命令行方式
Windows
gradlew clean
gradlew assemble
Linux/Mac
./gradlew clean
./gradlew assemble
Build > Clean Project