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/PreventDamageToTargetEffect.java

@@ -89,7 +89,7 @@ public class PreventDamageToTargetEffect extends PreventionEffectImpl {
         }
         sb.append(mode.getTargets().get(0).getTargetName());
         if (!duration.toString().isEmpty()) {
-            sb.append(" ");
+            sb.append(' ');
             if (duration.equals(Duration.EndOfTurn)) {
                 sb.append("this turn");
             } else {