title: ADD command failing while building dockerfile using docker-build-step plugin in jenkins
body: <p>The following is my DockerFile</p>
  
  <pre><code>FROM centos:centos6
  MAINTAINER Priyanka
  
  ################## Helpful utils
  RUN yum -y install sudo
  RUN yum -y install curl
  RUN yum -y install unzip
  
  ################## JDK7
  
  #Note that ADD uncompresses this tarball automatically
  ADD jdk-7u79-linux-x64.tar.gz /opt
  WORKDIR /opt/jdk1.7.0_79
  RUN alternatives --install /usr/bin/java java /opt/jdk1.7.0_79/bin/java 1
  RUN alternatives --install /usr/bin/jar jar /opt/jdk1.7.0_79/bin/jar 1
  RUN alternatives --install /usr/bin/javac javac /opt/jdk1.7.0_79/bin/javac 1
  RUN echo "JAVA_HOME=/opt/jdk1.7.0_79" &gt;&gt; /etc/environment
  ENV JAVA_OPTS -Xms1024m -Xmx4196m -XX:NewSize=256m -XX:MaxNewSize=356m -XX:PermSize=256m -XX:MaxPermSize=356m
  
  ################## TOMCAT
  
  #Note that ADD uncompresses this tarball automatically
  ADD apache-tomcat-7.0.67.tar.gz /usr/share
  WORKDIR /usr/share/
  RUN mv  apache-tomcat-7.0.67 tomcat7
  RUN echo "JAVA_HOME=/opt/jdk1.7.0_79/" &gt;&gt; /etc/default/tomcat7
  RUN groupadd tomcat
  RUN useradd -s /bin/bash -g tomcat tomcat
  RUN chown -Rf tomcat.tomcat /usr/share/tomcat7
  EXPOSE 8087
  
  ################## ROC Client War Download
  
  RUN curl -O http://10.113.57.164:8080/job/ROC4.0_Client/ws/spark-web/entrypoint/target/entrypoint.war
  RUN unzip entrypoint.war -d /usr/share/tomcat7/webapps/roc_client
  ADD validation-api-1.1.0.Final.jar /usr/share/tomcat7/webapps/roc_client/WEB-INF/lib/
  ADD validation-api-1.1.0.Final-sources.jar /usr/share/tomcat7/webapps/roc_client/WEB-INF/lib/
  RUN rm /usr/share/tomcat7/webapps/roc_client/WEB-INF/lib/validation-api-1.0.0.GA-sources.jar 
  RUN rm /usr/share/tomcat7/webapps/roc_client/WEB-INF/lib/validation-api-1.0.0.GA.jar
  
  ################## Tomcat launch
  
  CMD ["/usr/share/tomcat7/bin/catalina.sh","run"]
  </code></pre>
  
  <p>On building this file using docker-build-step in Jenkins the build fails with the following exception at ADD</p>
  
  <pre><code>Step 0 : FROM centos:centos6
  
   ---&gt; 3bbbf0aca359
  
  Step 1 : MAINTAINER Priyanka
  
   ---&gt; Using cache
  
   ---&gt; c8055ba8439a
  
  Step 2 : RUN yum -y install sudo
  
   ---&gt; Using cache
  
   ---&gt; 203da82ad2af
  
  Step 3 : RUN yum -y install curl
  
   ---&gt; Using cache
  
   ---&gt; c6cb08257236
  
  Step 4 : RUN yum -y install unzip
  
   ---&gt; Using cache
  
   ---&gt; 688620db641a
  
  Step 5 : ADD jdk-7u79-linux-x64.tar.gz /opt
  
  ERROR: Build step failed with exception
  java.lang.RuntimeException: java.lang.ClassCastException: org.glassfish.json.JsonObjectBuilderImpl$JsonObjectImpl cannot be cast to javax.json.JsonString
      at org.jenkinsci.plugins.dockerbuildstep.cmd.CreateImageCommand.execute(CreateImageCommand.java:139)
      at org.jenkinsci.plugins.dockerbuildstep.DockerBuilder.perform(DockerBuilder.java:75)
      at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
      at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:782)
      at hudson.model.Build$BuildExecution.build(Build.java:205)
      at hudson.model.Build$BuildExecution.doRun(Build.java:162)
      at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:534)
      at hudson.model.Run.execute(Run.java:1738)
      at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
      at hudson.model.ResourceController.execute(ResourceController.java:98)
      at hudson.model.Executor.run(Executor.java:410)
  Caused by: java.lang.ClassCastException: org.glassfish.json.JsonObjectBuilderImpl$JsonObjectImpl cannot be cast to javax.json.JsonString
      at org.glassfish.json.JsonObjectBuilderImpl$JsonObjectImpl.getJsonString(JsonObjectBuilderImpl.java:194)
      at org.glassfish.json.JsonObjectBuilderImpl$JsonObjectImpl.getString(JsonObjectBuilderImpl.java:199)
      at org.jenkinsci.plugins.dockerbuildstep.cmd.CreateImageCommand$1.callback(CreateImageCommand.java:123)
      at org.jenkinsci.plugins.dockerbuildstep.cmd.CreateImageCommand.readJsonStream(CreateImageCommand.java:161)
      at org.jenkinsci.plugins.dockerbuildstep.cmd.CreateImageCommand.execute(CreateImageCommand.java:115)
      ... 10 more
  Build step 'Execute Docker command' marked build as failure
  Finished: FAILURE
  </code></pre>
  
  <p>I have run this build many times and it ran successfully without any problem.I made some temporary changes to build configuration and reverted back. Since then it is throwing this  error.
  Tried removing off all the docker commands from the File and retained just one RUN command.Still the same issue.It is not able to run any docker commands.</p>