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)

Reproduce the problem by opening FirefoxDriver.java in the client project with the two pom.xml files described, then start with DocumentLifeCycleHandler.java and CodeLensHandler.java from the stack traces. Compare the client and server project setup and confirm that opening the client file no longer reports “empty does not exist” or fails to provide code lenses.