> 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:

![](https://2994090777-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZH2AGHzvPfBW7YdaaGc0%2Fuploads%2Fgit-blob-06db0cf7fac1f32f452be9ed9a15a497f54467d7%2Fhmfile_hash_8dd85f87.png?alt=media)

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

![](https://2994090777-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZH2AGHzvPfBW7YdaaGc0%2Fuploads%2Fgit-blob-c84d5e9415d7782f27935a864bc8ed0e1f748a93%2Fhmfile_hash_2fa60d65.png?alt=media)

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

![](https://2994090777-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZH2AGHzvPfBW7YdaaGc0%2Fuploads%2Fgit-blob-ee157a17d0fc9aa45cabf3fcd00b19ef57408ea5%2Fhmfile_hash_19db6032.png?alt=media)

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.

![](https://2994090777-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZH2AGHzvPfBW7YdaaGc0%2Fuploads%2Fgit-blob-16d377ab3dfd240b29a27f10ef5c17ccd564289a%2Fhmfile_hash_4fdf1b1f.png?alt=media)

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.

![](https://2994090777-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZH2AGHzvPfBW7YdaaGc0%2Fuploads%2Fgit-blob-b4c6e90c92953a730c8a7a4f6898e794cb3bc2fb%2Fhmfile_hash_a3f73a6d.png?alt=media)