Update modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java

Co-authored-by: Sergey Chugunov <sergey.chugunov@gmail.com>

Author: anton-vinogradov

modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java

@@ -93,7 +93,7 @@ public void checkConfiguration() {
             throw new IllegalStateException("Either set of datacenters or main datacenter should be specified.");
 
         if (dcs != null && dcs.isEmpty())
-            throw new IllegalStateException("Missing datacenters.");
+            throw new IllegalStateException("Please provide a non-empty set of datacenters.");
 
         if (mainDc != null && dcs != null && dcs.size() % 2 == 1)
             throw new IllegalStateException("Datacenters count must be even when main datacenter is set.");