Return error when invalid string is passed as a Run status CLI argument (#4212)

* removed redundnat null checks of nonnull values

* integrated suggestions

* removed local jenkins variable as suggested

* replaced null check with check for error object

core/src/main/java/hudson/ProxyConfiguration.java

@@ -380,7 +380,7 @@ public final class ProxyConfiguration extends AbstractDescribableImpl<ProxyConfi
     private static ProxyConfiguration _get() {
         JenkinsJVM.checkJenkinsJVM();
         // this code could be called between the JVM flag being set and theInstance initialized
-        Jenkins jenkins = Jenkins.get();
+        Jenkins jenkins = Jenkins.getInstanceOrNull();
         return jenkins == null ? null : jenkins.proxy;
     }