fix: Avoid NullPointerException in certain conn error cases (#68)

Motivation

In rare cases it's possible that the exception passed to the EtcdClient#reauthRequired() has CANCELLED gRPC code but no cause, which causes an NPE.

Modifications

Add null check to EtcdClient#reauthRequired()

Result

Avoid NPE

Author: njhill

src/main/java/com/ibm/etcd/client/EtcdClient.java

@@ -608,6 +608,9 @@ public boolean isClosed() {
     private long authFailRetryTime;
 
     protected static boolean reauthRequired(Throwable error) {
+        if (error == null) {
+            return false;
+        }
         Status status = Status.fromThrowable(error);
         Code code = status.getCode();
         return code == Code.UNAUTHENTICATED