diff --git a/ontolib-core/src/main/java/com/github/phenomics/ontolib/formats/hpo/HpoDiseaseAnnotation.java b/ontolib-core/src/main/java/com/github/phenomics/ontolib/formats/hpo/HpoDiseaseAnnotation.java
index 5c9dddc..c105e96 100644
--- a/ontolib-core/src/main/java/com/github/phenomics/ontolib/formats/hpo/HpoDiseaseAnnotation.java
+++ b/ontolib-core/src/main/java/com/github/phenomics/ontolib/formats/hpo/HpoDiseaseAnnotation.java
@@ -200,7 +200,7 @@ public String getOnsetModifier() {
   }
 
   /**
-   * @return Frequency modifier; optional, <code>null</code> when missing.
+   * @return Frequency modifier; returns "" empty string when not present
    */
   public String getFrequencyModifier() {
     return frequencyModifier;