ISPHttpClientConfiguration.jsonRequest is enabled, which requires the "OData-Version" header to be 3.0 or 4.0
What causes it and how to fix it:
- File upload via /Files/add: nometadata works under OData v4 — an empty OData-Version breaks SPFx when you leave out Content-Typenometadata + octet-stream under the default OData v4; an empty OData-Version without Content-Type throws inside SPHttpClient; plus the empty-filename mobile camera trapCause and fix →