This would start happening if the network connection between the Hydra server and the remote build server breaks after sucessfully importing at least one output of a derivation, but before having finished importing all outputs.
Fixes #816.
GPUIIYUKOCYHVF5VWXSGSW2LT6WWTQY6XZPWLFKZJJFIKHWO4Q2QC /* Note: we should only send the command to dump the storepath to the remote if the NAR is actually going to get readby the destination store, which won't happen if this pathis already valid on the destination store. Since thislambda function only gets executed if someone tries to readfrom source2, we will send the command from here ratherthan outside the lambda. */to << cmdDumpStorePath << localStore->printStorePath(path);to.flush();