> For the complete documentation index, see [llms.txt](https://help.auxalia.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.auxalia.com/plant-tools/plantexpresstools/how-to-use/off-page-connector-manager/usage/additional-use-cases/override-if-empty.md).

# Override if Empty

This chapter describes how the 'Override if Empty' options influences the mapping when connecting two OPCs.

The option 'Override if Empty' maps a value from one OPC to another if one OPC doesn't have a value independent of the 'Mapping/Propagation Direction'

For this example we use the following setup:

![](/files/gghUBKocd4FuPp1zAlbr)

The case we have here is, that connector #1 has a size but no spec, and connector #3 has a spec but no size.

![](/files/S7L7slGUv7bd3YW0LXwS)

Now we drag & drop connector #3 over #1.

![](/files/rhQTd2danCWjA6op2Bky)

We see, that independent of the drag & drop direction, the size was copied from connector #1 to #3, whereas spec was copied from #3 to #1.

![](/files/7QDFQQRY8ibGfvJsVEGb)

The matrix below shows what the result will be when using this option or not. Also in combination with AttributeFlow. The difference you can expect are within the red boxes.

![](/files/yqXkSorQIPUsq21lbNN2)