[JENKINS-53445] Trap unrecognized JVM version

Let's not fire an NPE when the plugin doesn't know the JVM and ByteCode
versions. Still marking the master-agent as incompatible to prevent any
potential issues.

src/main/java/hudson/plugin/versioncolumn/JVMVersionComparator.java

@@ -91,9 +91,16 @@ private int getMasterBytecodeMajorVersionNumber() {
 
     private boolean isAgentRuntimeCompatibleWithJenkinsBytecodeLevel(String agentMajorMinorVersion) {
         Integer masterBytecodeLevel = getMasterBytecodeMajorVersionNumber();
-        Integer agentVMMaxBytecodeLevel = JDK_VERSION_NUMBER_TO_BYTECODE_LEVEL_MAPPING.get(agentMajorMinorVersion);
-
-        return masterBytecodeLevel <= agentVMMaxBytecodeLevel;
+        try {
+            Integer agentVMMaxBytecodeLevel = JDK_VERSION_NUMBER_TO_BYTECODE_LEVEL_MAPPING.get(agentMajorMinorVersion);
+            return masterBytecodeLevel <= agentVMMaxBytecodeLevel;
+        } catch(NullPointerException e) {
+            LOGGER.log(Level.WARNING, Messages.JVMVersionMonitor_UnrecognizedAgentJVM(agentMajorMinorVersion));
+            /*
+             * Even if the version might be compatible, we still mark the node as incompatible to prevent potential issues.
+             */
+            return false;
+        }
     }
 
     public boolean isCompatible() {

src/main/resources/hudson/plugin/versioncolumn/Messages.properties

@@ -7,4 +7,6 @@ JVMVersionMonitor.OfflineCause=This node is offline because the JVM version of t
 JVMVersionMonitor.MarkedOffline=Making {0} offline temporarily due to using an incompatible JVM version between agent and master (master={1}, agent={2})
 JVMVersionMonitor.RUNTIME_GREATER_OR_EQUAL_MASTER_BYTECODE=Agent runtime must be greater or equal than the Master bytecode level (strongly recommended minimum)
 JVMVersionMonitor.MAJOR_MINOR_MATCH=Agent major.minor must be equal to Master major.minor JVM version (paranoid version)
-JVMVersionMonitor.EXACT_MATCH=Agent JVM version must be exactly the same as Master JVM version (paranoid++ version)
+JVMVersionMonitor.EXACT_MATCH=Agent JVM version must be exactly the same as Master JVM version (paranoid++ version)
+
+JVMVersionMonitor.UnrecognizedAgentJVM=The agent JVM version {0} is not recognized by the plugin. You might want to open a ticket for the maintainer to complete the compatibility list.

src/test/java/hudson/plugin/versioncolumn/JVMVersionComparatorTest.java

@@ -5,8 +5,11 @@
 import junitparams.Parameters;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.jvnet.hudson.test.Issue;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 @RunWith(JUnitParamsRunner.class)
@@ -104,4 +107,13 @@ public int get() {
                                             }).isNotCompatible());
     }
 
+    @Issue("JENKINS-53445")
+    @Test
+    public void shouldNotThrowNPEWhenJVMVersionIsNotRecognized() {
+        JVMVersionComparator jvmVersionComparator =
+              new JVMVersionComparator("99.9", "99.9",
+                    JVMVersionComparator.ComparisonMode.RUNTIME_GREATER_OR_EQUAL_MASTER_BYTECODE);
+        assertNotNull(jvmVersionComparator);
+        assertFalse(jvmVersionComparator.isCompatible());
+    }
 }