All 1-character strings converted to primitives

"b" + "r" now changed to 'b' + 'w'.  It's more straight-forward, and may cause perfomance improvements - character primitives allocation is faster and less expensive than string creation.

Mage/src/main/java/mage/abilities/effects/common/CantBeTargetedAttachedEffect.java

@@ -117,7 +117,7 @@ public class CantBeTargetedAttachedEffect extends ContinuousRuleModifyingEffectI
         sb.append(" can't be the target of ");
         sb.append(filterSource.getMessage());
         if (!duration.toString().isEmpty()) {
-            sb.append(" ");
+            sb.append(' ');
             if (duration.equals(Duration.EndOfTurn)) {
                 sb.append("this turn");
             } else {