diff --git a/src/mixins/WidgetMixin.js b/src/mixins/WidgetMixin.js
index cf85300f..53019adf 100644
--- a/src/mixins/WidgetMixin.js
+++ b/src/mixins/WidgetMixin.js
@@ -133,7 +133,15 @@ const WidgetMixin = {
     },
     /* Check if a value is an environment variable, return its value if so. */
     parseAsEnvVar(str) {
-      if (str.includes('VUE_APP_')) return process.env[str];
+      if (typeof str !== 'string') return str;
+      if (str.includes('VUE_APP_')) {
+        const envVar = process.env[str];
+        if (!envVar) {
+          this.error(`Environment variable ${str} not found`);
+        } else {
+          return envVar;
+        }
+      }
       return str;
     },
   },