PM Creating working copy empty does not exist

I am using vscode-java with selenium project.
After I cloned form https://github.com/SeleniumHQ/selenium.git,
I create 2 pom.xml files, one for /selenium/java/client, one for /selenium/java/server, as below.

pom.xml for client

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.seleniumhq</groupId>
  <artifactId>client</artifactId>
  <version>2.52.0</version>
  <build>
    <directory>${project.basedir}/build</directory>
    <outputDirectory>${project.build.directory}/production</outputDirectory>
    <sourceDirectory>src</sourceDirectory>
    <testSourceDirectory>test</testSourceDirectory>
  </build>
</project>

pom.xlm for server

<project>
  <parent>
    <groupId>org.seleniumhq</groupId>
    <artifactId>client</artifactId>
    <version>2.52.0</version>
    <relativePath>../client/pom.xml</relativePath>
  </parent>
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.seleniumhq</groupId>
  <artifactId>server</artifactId>
  <version>2.52.0</version>
  <build>
    <directory>${project.basedir}/build</directory>
    <outputDirectory>${project.build.directory}/production</outputDirectory>
    <sourceDirectory>src</sourceDirectory>
    <testSourceDirectory>test</testSourceDirectory>
  </build>
</project>

when I open a java file in the server project, everything works well,
but when I open a java file in the client project,
PM Problem encountered like below.

[Error] Sep 25, 2016 4:17:27 PM Creating working copy 
empty does not exist
Java Model Exception: Java Model Status [empty does not exist]
    at org.eclipse.jdt.internal.core.JavaElement.newJavaModelException(JavaElement.java:566)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:247)
    at org.eclipse.jdt.internal.core.Openable.openAncestors(Openable.java:505)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:241)
    at org.eclipse.jdt.internal.core.Openable.openAncestors(Openable.java:505)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:241)
    at org.eclipse.jdt.internal.core.Openable.openAncestors(Openable.java:505)
    at org.eclipse.jdt.internal.core.CompilationUnit.openAncestors(CompilationUnit.java:1176)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:241)
    at org.eclipse.jdt.internal.core.JavaElement.openWhenClosed(JavaElement.java:579)
    at org.eclipse.jdt.internal.core.JavaElement.getElementInfo(JavaElement.java:316)
    at org.eclipse.jdt.internal.core.JavaElement.getElementInfo(JavaElement.java:302)
    at org.eclipse.jdt.internal.core.Openable.getBuffer(Openable.java:285)
    at org.jboss.tools.vscode.java.handlers.DocumentLifeCycleHandler.handleOpen(DocumentLifeCycleHandler.java:142)
    at org.jboss.tools.vscode.java.handlers.DocumentLifeCycleHandler.access$1(DocumentLifeCycleHandler.java:126)
    at org.jboss.tools.vscode.java.handlers.DocumentLifeCycleHandler$OpenHandler$1.run(DocumentLifeCycleHandler.java:75)
    at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2240)
    at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2262)
    at org.jboss.tools.vscode.java.handlers.DocumentLifeCycleHandler$OpenHandler.handle(DocumentLifeCycleHandler.java:72)
    at org.jboss.tools.vscode.java.handlers.DocumentLifeCycleHandler$OpenHandler.handle(DocumentLifeCycleHandler.java:1)
    at org.jboss.tools.langs.base.LSPServer.dispatchNotification(LSPServer.java:222)
    at org.jboss.tools.langs.base.LSPServer.messageReceived(LSPServer.java:156)
    at org.jboss.tools.langs.transport.AbstractConnection$DispatcherThread.run(AbstractConnection.java:32)

[Error] Sep 25, 2016 4:17:27 PM Problem getting code lenses forFirefoxDriver.java
empty does not exist
Java Model Exception: Java Model Status [empty does not exist]
    at org.eclipse.jdt.internal.core.JavaElement.newJavaModelException(JavaElement.java:566)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:247)
    at org.eclipse.jdt.internal.core.Openable.openAncestors(Openable.java:505)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:241)
    at org.eclipse.jdt.internal.core.Openable.openAncestors(Openable.java:505)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:241)
    at org.eclipse.jdt.internal.core.Openable.openAncestors(Openable.java:505)
    at org.eclipse.jdt.internal.core.CompilationUnit.openAncestors(CompilationUnit.java:1176)
    at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:241)
    at org.eclipse.jdt.internal.core.JavaElement.openWhenClosed(JavaElement.java:579)
    at org.eclipse.jdt.internal.core.JavaElement.getElementInfo(JavaElement.java:316)
    at org.eclipse.jdt.internal.core.JavaElement.getElementInfo(JavaElement.java:302)
    at org.eclipse.jdt.internal.core.JavaElement.getChildren(JavaElement.java:257)
    at org.jboss.tools.vscode.java.handlers.CodeLensHandler.getCodeLensSymbols(CodeLensHandler.java:124)
    at org.jboss.tools.vscode.java.handlers.CodeLensHandler.access$0(CodeLensHandler.java:122)
    at org.jboss.tools.vscode.java.handlers.CodeLensHandler$CodeLensProvider.handle(CodeLensHandler.java:47)
    at org.jboss.tools.vscode.java.handlers.CodeLensHandler$CodeLensProvider.handle(CodeLensHandler.java:1)
    at org.jboss.tools.langs.base.LSPServer.dispatchRequest(LSPServer.java:210)
    at org.jboss.tools.langs.base.LSPServer.messageReceived(LSPServer.java:165)
    at org.jboss.tools.langs.transport.AbstractConnection$DispatcherThread.run(AbstractConnection.java:32)

Tái hiện vấn đề bằng cách mở FirefoxDriver.java trong dự án client với hai tệp pom.xml đã mô tả, sau đó bắt đầu với DocumentLifeCycleHandler.java và CodeLensHandler.java từ các stack trace. So sánh thiết lập của dự án client và server, đồng thời xác nhận rằng việc mở tệp client không còn báo cáo “empty does not exist” hoặc không cung cấp được code lenses nữa.