incompatible with flatpak: The java.home variable defined in VS Code settings points to a missing folder

[vscode installed by flatpak can not access JAVA_HOME]

I'm not sure is this a bug of vscode-java or flatpack.
Note: flatpak run vscode in a isolated environment.

Environment

• Operating System: Ubuntu 18.04 X86_64
• JDK version: oracle JDK 1.8
• Visual Studio Code version:
• Java extension version:

Steps To Reproduce

1. [step 1]
   install flatpak: https://flatpak.org
   install vscode from: https://flathub.org/apps/details/com.visualstudio.code
2. [step 2]
   install vscode-java and set correct JAVA_HOME/java.home
   try to open/run java code

[attach a sample project reproducing the error]
attach logs

Current Result

The java.home/JAVA_HOME variable defined in VS Code settings points to a missing folder

Expected Result

run normal without error.

Additional Informations

JAVA_HOME=/usr/lib/jvm/java-8-oracle

Every thing is OK when run vscode which is installed by .deb file (download from https://code.visualstudio.com/docs/setup/linux).

No source file or test is identified. Reproduce the issue with the Flatpak VS Code installation, vscode-java, and the stated JAVA_HOME/java.home setting; compare it with the .deb installation and verify completion when Java opens or runs without a missing-folder error.