1 files changed, 8 insertions, 1 deletions

diff --git a/lib/Monitoring/Plugin/Performance.pm b/lib/Monitoring/Plugin/Performance.pm
index f1e7a16..0871042 100644
--- a/lib/Monitoring/Plugin/Performance.pm
+++ b/lib/Monitoring/Plugin/Performance.pm
@@ -64,9 +64,16 @@ sub perfoutput {
         if ($label =~ / /) {
                 $label = "'$label'";
         }
+        
+        my $value = $self->value;
+        # To prevent invalid output, we change empty value to value "U"
+        if ($value eq '') {
+                $value = 'U';
+    }
+    
     my $out = sprintf "%s=%s%s;%s;%s;%s;%s",
         $label,
-        $self->value,
+        $value,
         $self->_nvl($self->uom),
         $self->_nvl($self->warning),
         $self->_nvl($self->critical),