public List<SQLNotNullConstraint> build(Configuration conf) throws MetaException {
    checkBuildable("not_null_constraint", conf);
    List<SQLNotNullConstraint> uc = new ArrayList<>(columns.size());
    for (String column : columns) {
      SQLNotNullConstraint c = new SQLNotNullConstraint(catName, dbName, tableName, columns.get(0),
          constraintName, enable, validate, rely);
      uc.add(c);
    }
    return uc;
  }
Builder for {@link SQLNotNullConstraint}.  Only requires what {@link ConstraintBuilder} requires.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/client/builder/SQLNotNullConstraintBuilder.java