if a.IsNull() {
			// Missing is null
			return v.IsNull() || v.IsMissing(), nil
		}
		if a.IsMissing() {
			return v.IsMissing(), nil
		}
		// Forward to Equal
		op = opEq
	case opIsNot:
		if a.IsNull() {
			// Missing is not null
			return !v.IsNull() && !v.IsMissing(), nil
		}
		if a.IsMissing() {
			return !v.IsMissing(), nil
		}
		// Forward to not equal.
		op = opIneq
	default: