Niagara Static Mesh module says "Illegal TEXT reference"

In the Sample Static Mesh module,
The “Source” option cannot be set (click on it, and choose an StaticMesh actor that uses that mesh).
The output log says: “LogProperty: Warning: Illegal TEXT reference to a private object in external package (StaticMeshActor /Game/NiagaraTest/NiagaraMap.NiagaraMap:PersistentLevel.tess-plane30_w_vc_5) from referencer (NiagaraDataInterfaceStaticMesh /Engine/Transient.NiagaraEmitter_3:NiagaraScriptSource_0.NiagaraGraph_0.NiagaraNodeInput_6.StaticMesh). Import failed…

My mesh is a simple plane with vertex colors. What’s missing here?

We could probably name things better. Source is meant to be set from within the map the system is used in. Usually, you’d make it a User variable and you can set it in the regular property editor in the level. Default Mesh should probably be called Preview mesh as it is meant to be a standalone asset that you can use when tweaking the system in the editor.