Attachments not importing through CSV for the extracted issues from Next Gen

[Kaustubh Sarnaik]

Attachments not browsing when doing a csv Import in a classic project for the issues which were  in first place extracted from the Next Gen project. 

Steps : 

1) Exporting issues from Next Gen 

2) Importing through System CSV 

3) Mapping Attachment to Attachments 

4) Issue get imported but attachments cannot be opened.