UPDATE:

I can circumvent this issue by using /job/JOBNAME/buildWithParameters instead. Deprioritized.

When I try to specify the label parameter in launching my jenkins job like this:

curl --silent --show-error --data 'json={"parameter":[

{"name":"NODE_LABEL","value":"LABEL"}

]&Submit=Build' http://jenkins:8888/job/JOBNAME/build

It seems to ignore it and I end up with an error message like this:

00:00:00.018 FATAL: Null value not allowed as an environment variable: NODE_LABEL
00:00:00.018 java.lang.IllegalArgumentException: Null value not allowed as an environment variable: NODE_LABEL
00:00:00.019 at hudson.EnvVars.put(EnvVars.java:172)
00:00:00.019 at org.jvnet.jenkins.plugins.nodelabelparameter.LabelParameterValue.buildEnvVars(LabelParameterValue.java:71)
00:00:00.019 at hudson.model.ParametersAction.buildEnvVars(ParametersAction.java:82)
00:00:00.019 at hudson.model.AbstractBuild.getEnvironment(AbstractBuild.java:961)
00:00:00.019 at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:776)
00:00:00.019 at hudson.model.AbstractProject.checkout(AbstractProject.java:1353)
00:00:00.019 at hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild.java:689)
00:00:00.019 at jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:88)
00:00:00.019 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:594)
00:00:00.019 at hudson.model.Run.execute(Run.java:1567)
00:00:00.019 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
00:00:00.019 at hudson.model.ResourceController.execute(ResourceController.java:88)
00:00:00.019 at hudson.model.Executor.run(Executor.java:237)