Yet more test fixes

Author: atris

modules/ingest-common/src/main/java/org/opensearch/ingest/common/HierarchicalRoutingProcessor.java

@@ -80,6 +80,10 @@ public IngestDocument execute(IngestDocument document) throws Exception {
             return document;
         }
 
+        if (pathValue == null) {
+            throw new IllegalArgumentException("field [" + pathField + "] doesn't exist");
+        }
+
         String path = pathValue.toString();
         if (Strings.isNullOrEmpty(path)) {
             if (ignoreMissing) {