Overview:
For the MARC bib records generated on the fly, the Instances identifiers  should be set the following way: "Linking ISSN" set to 022 \ \ $l and "Invalid ISBN" set to 020 \ \ $z 
UPD: also reproduced for :
"Invalid ISSN" 022 \ \ $z without  {}"ISSN"{*}{*}{*}{*}
"Cancelled GPO Item number" 074 \ \ $z without "GPO Item number" 074 \ \ $a

But these identifiers are missed in .mrc file in case Instance has no  ISSN (022$a) or  ISBN (020$a)
The issue is reproduced only for MARC bib records generated on the fly

Steps to Reproduce:

1. Using Default instance job profile export FOLIO Instance with associated identifiers:

• "Linking ISSN" 

• "Invalid ISBN"

1. Open .mrc file with generated instances => Check fields: 022$l and  020$z

Expected Results:

"Linking ISSN" set to 022$l (first indicator is blank, second indicator is blank)

"Invalid ISBN" set to 020$z (first indicator is blank, second indicator is blank)

Actual Results:

Both identifiers are missed in .mrc file
The identifiers appears only in case Instance has in addition  ISSN (022$a) /  ISBN (020$a)

Additional Information:
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