message: add CifField.ofUndefined
diff: @@ -265,6 +265,10 @@ export namespace CifField {
  toFloatArray: params => ColumnHelpers.createAndFillArray(rowCount, float, params)
  };
  }
  +
  + export function ofUndefined(rowCount: number, schema: Column.Schema): CifField {
  + return ofColumn(Column.Undefined(rowCount, schema));
  + }
  }
  export function tensorFieldNameGetter(field: string, rank: number, zeroIndexed: boolean, namingVariant: 'brackets' | 'underscore') {
  