`DagsterStepOutputNotFoundError` for `op` which yields `Asse

Question

`DagsterStepOutputNotFoundError` for `op` which yields `AssetMaterialization` I have an `op` which doesn t have an output I have added yielding of an `AssetMaterialization` and now I m getting `DagsterStepOutputNotFoundError` I ve tried adding `yield` `yield Output ` `yield Nothing` I m on `0 13 9` What does the `op` need yield in addition to the `AssertMaterialization`

Stefan Adelbert · Answer

My solution to this was ```yield Output None ``` I understand that as soon as something is being explicitly yielded from an `op` e g `AssetMaterialization` the implicit conversion of the `op` return value maybe `None` if the `op` returns nothing to an `Output` can t happen In this case it s required to explicitly yield some `Output` even if it s `Output None ` <https docs dagster io concepts ops jobs graphs op events outputs>

prha · Answer

Yes that s exactly right The implicit return value of a function that does not return anything is `None` Also as soon as your op yields an explicit event it must also yield an explicit `Output` <https docs dagster io concepts assets asset materializations yielding an assetmaterialization from a op>

Stefan Adelbert · Answer

< prha> Thanks