diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/ltr/FieldValueFeatureExtractor.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/ltr/FieldValueFeatureExtractor.java
index 5a2e3d29df94..9014c79f0af9 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/ltr/FieldValueFeatureExtractor.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/ltr/FieldValueFeatureExtractor.java
@@ -53,7 +53,10 @@ public void setNextReader(LeafReaderContext segmentContext) {
     public void addFeatures(Map<String, Object> featureMap, int docId) throws IOException {
         Source source = sourceLookup.getSource(this.segmentContext, docId);
         for (FieldValueFetcher vf : this.valueFetcherList) {
-            featureMap.put(vf.fieldName(), vf.valueFetcher().fetchValues(source, docId, new ArrayList<>()).get(0));
+            List<Object> values = vf.valueFetcher().fetchValues(source, docId, new ArrayList<>());
+            if (values.isEmpty() == false) {
+                featureMap.put(vf.fieldName(), values.get(0));
+            }
         }
     }