private void checkStemmingForIndexFields(String indexName, List<SDField> fields) {
        Stemming stemming = null;
        SDField stemmingField = null;
        for (SDField field : fields) {
            if (stemming == null && stemmingField==null) {
                stemming = field.getStemming(schema);
                stemmingField = field;
            } else if (stemming != field.getStemming(schema)) {
                deployLogger.logApplicationPackage(Level.WARNING, "Field '" + field.getName() + "' has " + field.getStemming(schema) +
                                                                  ", whereas field '" + stemmingField.getName() + "' has " + stemming +
                                                                  ". All fields indexing to the index '" + indexName + "' must have the same stemming." +
                                                                  " This should be corrected as it will make indexing fail in a few cases.");
            }
        }
    }
Class resolving conflicts when fields with different stemming-settings are
combined into the same index
config-model/src/main/java/com/yahoo/schema/processing/multifieldresolver/StemmingResolver.java