public void setStemming(Stemming stemming) {
        this.stemming = Objects.requireNonNull(stemming, "Stemming cannot be null");
    }
Sets the stemming default of fields. Default is ALL

@param stemming set default stemming for this schema
@throws NullPointerException if this is attempted set to null
config-model/src/main/java/com/yahoo/schema/Schema.java