Check nil error in IsProbableEOF()

staging/src/k8s.io/apimachinery/pkg/util/net/http.go

@@ -61,6 +61,9 @@ func JoinPreservingTrailingSlash(elem ...string) string {
 // differentiate probable errors in connection behavior between normal "this is
 // disconnected" should use the method.
 func IsProbableEOF(err error) bool {
+	if err == nil {
+		return false
+	}
 	if uerr, ok := err.(*url.Error); ok {
 		err = uerr.Err
 	}