1 files changed, 1 insertions, 1 deletions
diff --git a/lib/Spreadsheet/ParseXLSX.pm b/lib/Spreadsheet/ParseXLSX.pm
index cf9319a..26e591e 100644
--- a/lib/Spreadsheet/ParseXLSX.pm
+++ b/lib/Spreadsheet/ParseXLSX.pm
@@ -921,7 +921,7 @@ sub _color {
                 $color = "#$theme";
             }
             else {
-                return;
+                return undef;
             }
         }