[JENKINS-15094] - Unit tests for the issue

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
[FIXED JENKINS-15094] - Handle null parameter values in BuildCommand (CLI) and Parameter classes (CLI).

The change adds missing checks for null ParameterValue, which may be passed from the CLI.
It prevents the death of Jenkins executors during the canTake() check of node labels.

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>