Default to empty DC failover preferred remoted DCs

Author: alexsa

core/src/main/java/com/datastax/oss/driver/api/core/config/OptionsMap.java

@@ -381,8 +381,7 @@ protected static void fillWithDriverDefaults(OptionsMap map) {
     map.put(TypedDriverOption.LOAD_BALANCING_DC_FAILOVER_MAX_NODES_PER_REMOTE_DC, 0);
     map.put(TypedDriverOption.LOAD_BALANCING_DC_FAILOVER_ALLOW_FOR_LOCAL_CONSISTENCY_LEVELS, false);
     map.put(TypedDriverOption.METRICS_GENERATE_AGGREGABLE_HISTOGRAMS, true);
-    map.put(
-        TypedDriverOption.LOAD_BALANCING_DC_FAILOVER_PREFERRED_REMOTE_DCS, ImmutableList.of(""));
+    map.put(TypedDriverOption.LOAD_BALANCING_DC_FAILOVER_PREFERRED_REMOTE_DCS, ImmutableList.of());
   }
 
   @Immutable

core/src/main/resources/reference.conf

@@ -580,7 +580,7 @@ datastax-java-driver {
       # Required: no
       # Modifiable at runtime: no
       # Overridable in a profile: no
-      preferred-remote-dcs = [""]
+      preferred-remote-dcs = []
     }
   }