Fix clearing keywords

Bugzilla/Bug.pm

@@ -1869,7 +1869,7 @@ sub _set_keywords
             my $keyword_string = $data->{keywords};
             $keyword_string =~ s/^[\s,]+//s;
             $keyword_string =~ s/[\s,]+$//s;
-            if ($keyword_string)
+            if ($keyword_string ne '')
             {
                 $keyword_string = [ split /[\s,]*,[\s,]*/, $keyword_string ];
                 my $kw = Bugzilla::Keyword->match({ name => $keyword_string });
@@ -1888,6 +1888,10 @@ sub _set_keywords
                 }
                 $new = [ values %$kw ];
             }
+            else
+            {
+                $new = [];
+            }
         }
         # Make sure we retain the sort order.
         $new = [ sort { lc($a->name) cmp lc($b->name) } @$new ];

process_bug.cgi

@@ -351,7 +351,7 @@ elsif (defined $ARGS->{dependson} || defined $ARGS->{blocked})
 }
 
 my $any_keyword_changes;
-if ($ARGS->{keywords})
+if (exists $ARGS->{keywords})
 {
     foreach my $b (@bug_objects)
     {