patch applied for issue 66

Dapper/SqlMapper.cs

@@ -431,9 +431,12 @@ public static IEnumerable<T> Query<T>(this IDbConnection cnn, string sql, object
             }
 
             // nice and simple
-            identity = new Identity(sql, commandType, cnn, null, (object)param == null ? null : ((object)param).GetType(), null);
+            if ((object)param != null)
+            {
+                identity = new Identity(sql, commandType, cnn, null, (object) param == null ? null : ((object) param).GetType(), null);
                 info = GetCacheInfo(identity);
-            return ExecuteCommand(cnn, transaction, sql, info.ParamReader, (object)param, commandTimeout, commandType);
+            }
+            return ExecuteCommand(cnn, transaction, sql, (object)param == null ? null : info.ParamReader, (object)param, commandTimeout, commandType);
         }
 #if !CSHARP30
         /// <summary>