diff --git a/src/classes.ts b/src/classes.ts
index 3e57e6732..5cc65c25c 100644
--- a/src/classes.ts
+++ b/src/classes.ts
@@ -519,7 +519,7 @@ export class Pronoun {
         }
 
         const value = this.morphemes[morpheme];
-        if (value === null) {
+        if (value === null || value === undefined) {
             return null;
         }