Fix for NPE when is_serverless is not provided by user

Author: bhvkshah

src/main/java/com/amazon/redshift/core/IamHelper.java

@@ -123,7 +123,7 @@ public static RedshiftProperties setIAMProperties(RedshiftProperties info, Redsh
 
       String host = RedshiftConnectionImpl.getOptionalConnSetting(RedshiftProperty.HOST.getName(), info);
       String userSetServerless = RedshiftConnectionImpl.getOptionalConnSetting(RedshiftProperty.IS_SERVERLESS.getName(), info);
-      Boolean hasUserSetServerless = userSetServerless.equalsIgnoreCase("true");
+      Boolean hasUserSetServerless = "true".equalsIgnoreCase(userSetServerless);
       String acctId = null;
       String workGroup = null;