Injecting environment variable via envinject plugin which is sucessfull, later failed while using that variable in copy artifact plugin.

find stracktrace below:

[EnvInject] - Injecting environment variables from a build step.
[EnvInject] - Injecting as environment variables the properties content
DOWNSTREAM_JOB_BUILD_NUMBER1=$DOWNSTREAM_JOB_BUILD_NUMBER

[EnvInject] - Variables injected successfully.
FATAL: For input string: "$DOWNSTREAM_JOB_BUILD_NUMBER"
java.lang.NumberFormatException: For input string: "$DOWNSTREAM_JOB_BUILD_NUMBER"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:449)
at java.lang.Integer.parseInt(Integer.java:499)
at hudson.plugins.copyartifact.SpecificBuildSelector.getBuild(SpecificBuildSelector.java:51)
at hudson.plugins.copyartifact.CopyArtifact.perform(CopyArtifact.java:176)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:697)
at hudson.model.Build$RunnerImpl.build(Build.java:178)
at hudson.model.Build$RunnerImpl.doRun(Build.java:139)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:467)
at hudson.model.Run.run(Run.java:1404)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:238)