Fixed a NullReferenceException when merging DynamicParameters

Dapper/SqlMapper.cs

@@ -1978,7 +1978,7 @@ class ParamInfo
         /// <summary>
         /// construct a dynamic parameter bag
         /// </summary>
-        /// <param name="template">can be an anonymous type of a DynamicParameters bag</param>
+        /// <param name="template">can be an anonymous type or a DynamicParameters bag</param>
         public DynamicParameters(object template)
         {
             if (template != null)
@@ -1989,7 +1989,7 @@ public DynamicParameters(object template)
 
         /// <summary>
         /// Append a whole object full of params to the dynamic
-        /// EG: AddParams(new {A = 1, B = 2}) // will add property A and B to the dynamic
+        /// EG: AddDynamicParams(new {A = 1, B = 2}) // will add property A and B to the dynamic
         /// </summary>
         /// <param name="param"></param>
         public void AddDynamicParams(
@@ -2023,6 +2023,7 @@ dynamic param
 
                     if (subDynamic.templates != null)
                     {
+                        templates = templates ?? new List<object>();
                         foreach (var t in subDynamic.templates)
                         {
                             templates.Add(t);