Use the nodebox as selection box if it's not set manually

builtin/misc_register.lua

@@ -103,6 +103,10 @@ function minetest.register_item(name, itemdef)
 
 	-- Apply defaults and add to registered_* table
 	if itemdef.type == "node" then
+		-- Use the nodebox as selection box if it's not set manually
+		if itemdef.drawtype == "nodebox" and not itemdef.selection_box then
+			itemdef.selection_box = itemdef.node_box
+		end
 		setmetatable(itemdef, {__index = minetest.nodedef_default})
 		minetest.registered_nodes[itemdef.name] = itemdef
 	elseif itemdef.type == "craft" then

doc/lua_api.txt

@@ -1589,6 +1589,7 @@ Node definition (register_node)
     damage_per_second = 0, -- If player is inside node, this damage is caused
     node_box = {type="regular"}, -- See "Node boxes"
     selection_box = {type="regular"}, -- See "Node boxes"
+    ^ If drawtype "nodebox" is used and selection_box is nil, then node_box is used
     legacy_facedir_simple = false, -- Support maps made in and before January 2012
     legacy_wallmounted = false, -- Support maps made in and before January 2012
     sounds = {