Prevents "use of uninitialized value" warnings when the
CGI is called with broken undefined GET parameters.

Signed-off-by: Leo-Andres Hofmann <hofmann(a)leo-andres.de>
---
 html/cgi-bin/getrrdimage.cgi | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/html/cgi-bin/getrrdimage.cgi b/html/cgi-bin/getrrdimage.cgi
index 26e026bba..6ec91cc92 100644
--- a/html/cgi-bin/getrrdimage.cgi
+++ b/html/cgi-bin/getrrdimage.cgi
@@ -44,9 +44,9 @@ my @supported_origins = ("entropy.cgi", "hardwaregraphs.cgi", "media.cgi",
 my $uri = URI->new($ENV{'REQUEST_URI'});
 my %query = $uri->query_form;
 
-my $origin = lc $query{'origin'}; # lower case
-my $graph = $query{'graph'};
-my $range = lc $query{'range'}; # lower case
+my $origin = lc ($query{'origin'} // ''); # lower case
+my $graph = $query{'graph'} // '';
+my $range = lc ($query{'range'} // ''); # lower case
 
 # Check parameters
 unless(($origin =~ /^\w+?\.cgi$/) && ($graph =~ /^[\w\-.,; ]+?$/) && ($range ~~ @Graphs::time_ranges)) {
-- 
2.27.0.windows.1