Absence of error type: #NULL

[aninde]

Description

Based on the requirements we should support error type #Null.

Steps to reproduce

src/Cell.ts

/**
 * Possible errors returned by our interpreter.
 */
export enum ErrorType {
  /** Division by zero. */
  DIV_BY_ZERO = 'DIV_BY_ZERO',
  /** Unknown function name. */
  NAME = 'NAME',
  VALUE = 'VALUE',
  NUM = 'NUM',
  NA = 'NA',
  /** Cyclic dependency. */
  CYCLE = 'CYCLE',
  /* Wrong address reference. */
  REF = 'REF',
}

Links

https://www.oasis-open.org/committees/download.php/16826/openformula-spec-20060221.html#Error

[wojciechczerniak]

Please use the newer version of the spec: https://docs.oasis-open.org/office/OpenDocument/v1.3/csprd02/part4-formula/OpenDocument-v1.3-csprd02-part4-formula.html#__RefHeading__1017966_715980110

[wojciechczerniak]

Blocked by #15. Needed only for union reference, when union result is empty.