docs: private void indexMissingFields() {
        for (FieldDescriptor fieldDescriptor : messageContext.getMessageDescriptor().getFields()) {
           if (!messageContext.isFieldMarked(fieldDescriptor.getNumber())) {
              Object defaultValue = fieldDescriptor.getJavaType() == JavaType.MESSAGE
                    || fieldDescriptor.hasDefaultValue() ? fieldDescriptor.getDefaultValue() : null;
              IndexingMetadata indexingMetadata = messageContext.getMessageDescriptor().getProcessedAnnotation(IndexingMetadata.INDEXED_ANNOTATION);
              FieldMapping fieldMapping = indexingMetadata != null ? indexingMetadata.getFieldMapping(fieldDescriptor.getName()) : null;
              if (indexingMetadata == null && isLegacyIndexingEnabled || fieldMapping != null && fieldMapping.index()) {
                 addFieldToDocument(fieldDescriptor, defaultValue, fieldMapping);
              }
           }
        }
     }