diff --git a/libraries/deno-commons-mod.ts b/libraries/deno-commons-mod.ts
index 51feead..b6082c9 100644
--- a/libraries/deno-commons-mod.ts
+++ b/libraries/deno-commons-mod.ts
@@ -17,12 +17,15 @@ export function compareVersion(ver1: string, ver2: string): 0 | 1 | -1 {
     return 0;
 }
 
-export function isOn(val: string): boolean {
-    const lowerVal = (val == null) ? val : val.toLowerCase();
+export function isOn(val: string | undefined): boolean {
+    if ((val === null) || (val === undefined)) {
+        return false;
+    }
+    const lowerVal = val.toLowerCase();
     return lowerVal === "on" || lowerVal === "yes" || lowerVal === "1" ||
         lowerVal === "true";
 }
 
-export function isEnvOn(envKey: string): string | undefined {
-    return Deno.env.get(envKey);
+export function isEnvOn(envKey: string): boolean {
+    return isOn(Deno.env.get(envKey));
 }