trace-cmd/doc: Fail if manpage/docbook.xsl is not found

Fail if the docbook.xsl is not found. Currently it fails if
the file does not exist, but passing in a blank string does not
produce an error.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/Documentation/Makefile b/Documentation/Makefile
index be3711f..b59370e 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -17,7 +17,7 @@ else
 endif
 
 define manpage.xsl
-        if [ ! -f ${MANPAGE_DOCBOOK_XSL} ]; then                \
+        if [ -z ${MANPAGE_DOCBOOK_XSL} ]; then                  \
                 echo "*********************************";       \
                 echo "** No docbook.xsl is installed **";       \
                 echo "** Can't make man pages        **";       \