do not allow to merge map with non-map nodes
do not allow to merge map with non-map nodes

this may modify a sequence into a map and in particular
break filters

tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,tangrams/tangram-es