Update callers of httputils.ReportError to specify message

go/httputils/http.go

Index: go/httputils/http.go
diff --git a/go/httputils/http.go b/go/httputils/http.go
index 6a1ba310464dcdde753f4f479a4d07e8ab5df4ff..738854e441058d0652c4e36a24824d9bc4e23c2c 100644
--- a/go/httputils/http.go
+++ b/go/httputils/http.go
@@ -168,10 +168,16 @@ func (t *BackOffTransport) RoundTrip(req *http.Request) (*http.Response, error)
 // be also useful if we could specify a return status explicitly.
 
 // ReportError formats an HTTP error response and also logs the detailed error message.
+// The message parameter is returned in the HTTP response. If it is not provided then
+// "Unknown error" will be returned instead.
 func ReportError(w http.ResponseWriter, r *http.Request, err error, message string) {
 	glog.Errorln(message, err)
 	if err != io.ErrClosedPipe {
-		http.Error(w, message, 500)
+		httpErrMsg := message
+		if message == "" {
+			httpErrMsg = "Unknown error"
+		}
+		http.Error(w, httpErrMsg, 500)
 	}
 }