Our nullability processor has logic that identifies string concatenation, and if one side is nullable, adds a COALESCE to an empty string. IIUC this is inconsistent with the rest of EF's behavior: we ...

In if: expressions, steps.check.outputs.rebuild works because it's being evaluated in a boolean context, where "true" (a non-empty string) is truthy. But in a with: input (like passing build: $ { { ...