anchor.diff:  ARG SPARK_VERSION
   ARG JDK_VERSION
   ARG JDK_URL
  +ARG GITHUB_USERNAME
  +ARG GITHUB_TOKEN
   ENV SPARK_VERSION       ${SPARK_VERSION}
   ENV JAVA_HOME           /opt/jdk$JDK_VERSION
   ENV PATH                ${JAVA_HOME}/bin:${PATH}
  
positive.code: ARG TINI_VERSION=v0.18.0
  ARG JDK_VERSION=8u192
  ARG JDK_URL=your_jdk_url
  
  # stage.1 graphene
  FROM ubuntu:18.04 AS graphene
  
negative.code:     ls /opt
  # spark modification
  RUN cd /opt && \
      git clone https://$GITHUB_USERNAME:$GITHUB_TOKEN@github.com/analytics-zoo/spark.git && \
      cd spark && \
      git checkout branch-3.1.2 && \
      git status && \
  