src/de/steamwar/command/AbstractTypeMapper.java

@@ -57,6 +57,6 @@ public interface AbstractTypeMapper<K, T> extends AbstractValidator<K, T> {
      * Returning null and the empty string are equivalent.
      */
     default String normalize(K sender, String s) {
-        return s;
+        return null;
     }
 }

testsrc/de/steamwar/command/CacheCommand.java

@@ -51,11 +51,6 @@ public class CacheCommand extends TestSWCommand {
             public Collection<String> tabCompletes(String sender, PreviousArguments previousArguments, String s) {
                 return Arrays.asList(count.getAndIncrement() + "");
             }
-
-            @Override
-            public String normalize(String sender, String s) {
-                return "";
-            }
         };
     }
 }