Using the syntax $NAME or ${NAME}
  (%NAME% on Windows), these variables can be used in job
  configurations, or from process launched by a build.
  
  Jenkins also supports a special syntax, BASE+EXTRA, which allows
  you to add multiple key-value pairs here, which will be prepended to an
  existing environment variable.
  
  For example, if you have a machine which has PATH=/usr/bin, you
  could add to the standard path by defining an environment variable here, with
  the name PATH+LOCAL_BIN and value /usr/local/bin.
  
  This would result in PATH=/usr/local/bin:/usr/bin being exported
  during builds executed on this machine.
  PATH+LOCAL_BIN=/usr/local/bin will also be exported.
  
  Multiple entries are prepended to the "base" variable according to the
  alphabetical order of the "extra" part  of the name.
  
If the Value is empty or whitespace-only, it will not be added to the environment, nor will it override or unset any environment variable with the same name that may already exist (e.g. a variable defined by the system).