GH-37 Fix shardKeyParameters null check

Author: AlexanderYastrebov

src/main/java/de/zalando/sprocwrapper/proxy/StoredProcedure.java

@@ -221,7 +221,7 @@ private static int[] createTypes(final List<StoredProcedureParameter> params) {
     }
 
     public int getShardId(final Object[] objs) {
-        if (shardKeyParameters == null) {
+        if (shardKeyParameters.isEmpty()) {
             return shardStrategy.getShardId(null);
         }