parquet-cli/src/main/java/org/apache/parquet/cli/csv/AvroCSV.java
private static Schema schema(Schema.Type type, boolean makeNullable) {
    Schema schema = Schema.create(type == null ? Schema.Type.STRING : type);
    if (makeNullable || type == null) {
      schema = Schema.createUnion(Lists.newArrayList(
          Schema.create(Schema.Type.NULL), schema));
    }
    return schema;
  }
private static Schema schema(Schema.Type type, boolean makeNullable) {
    Schema schema = Schema.create(type == null ? Schema.Type.STRING : type);
    if (makeNullable || type == null) {
      schema = Schema.createUnion(Lists.newArrayList(
          Schema.create(Schema.Type.NULL), schema));
    }
    return schema;
  }
Create a {@link Schema} for the given type. If the type is null,
the schema will be a nullable String. If isNullable is true, the returned
schema will be nullable.

@param type a {@link Schema.Type} compatible with {@code Schema.create}
@param makeNullable If {@code true}, the return type will be nullable
@return a {@code Schema} for the given {@code Schema.Type}
@see Schema#create(org.apache.avro.Schema.Type)