null check

Author: cgroschupp

src/main/java/hudson/plugins/ec2/SlaveTemplate.java

@@ -238,7 +238,7 @@ public class SlaveTemplate implements Describable<SlaveTemplate> {
 
     public HostKeyVerificationStrategyEnum hostKeyVerificationStrategy;
 
-    public final String staticHostKeys;
+    public String staticHostKeys;
 
     public final boolean associatePublicIp;
 

src/main/java/hudson/plugins/ec2/ssh/verifiers/CheckStaticStrategy.java

@@ -26,12 +26,14 @@
 import hudson.model.TaskListener;
 import hudson.plugins.ec2.EC2Cloud;
 import hudson.plugins.ec2.EC2Computer;
+import hudson.plugins.ec2.SlaveTemplate;
 import hudson.slaves.OfflineCause;
 
 import java.util.ArrayList;
 import java.util.Base64;
 
 import java.io.IOException;
+import java.util.Objects;
 import java.util.Scanner;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -51,9 +53,17 @@ public class CheckStaticStrategy extends SshHostKeyVerificationStrategy {
     private static final Logger LOGGER = Logger.getLogger(CheckStaticStrategy.class.getName());
 
     private ArrayList<HostKey> getStaticHostKeys(EC2Computer computer) {
-        ArrayList<HostKey> hostKeys = new ArrayList<>();
+        ArrayList<HostKey> hostKeys;
+        hostKeys = new ArrayList<>();
+
+        SlaveTemplate computerSlaveTemplate = computer.getSlaveTemplate();
+        if (computerSlaveTemplate == null) {
+            EC2Cloud.log(LOGGER, Level.WARNING, computer.getListener(), "slave template not exists");
+            return hostKeys;
+        }
+
+        Scanner scanner = new Scanner(computerSlaveTemplate.getStaticHostKeys());
 
-        Scanner scanner = new Scanner(computer.getSlaveTemplate().getStaticHostKeys());
         while (scanner.hasNextLine()) {
             String hostKeyString = scanner.nextLine();
             String[] hostKeyParts = hostKeyString.split(" ");
@@ -93,7 +103,7 @@ public boolean verify(EC2Computer computer, HostKey hostKey, TaskListener listen
             return false;
 
         } else if (existingHostKey.equals(hostKey)) {
-            EC2Cloud.log(LOGGER, Level.INFO, computer.getListener(), String.format("Connection allowed after the host key has been verified"));
+            EC2Cloud.log(LOGGER, Level.INFO, computer.getListener(), "Connection allowed after the host key has been verified");
             return true;
         } else {
             EC2Cloud.log(LOGGER, Level.WARNING, computer.getListener(), String.format("The SSH key (%s) presented by the instance has changed since first saved (%s). The connection to %s is closed to prevent a possible man-in-the-middle attack", hostKey.getFingerprint(), existingHostKey.getFingerprint(), computer.getName()));