Describe the bug
The error Interface\AddOns\GSE\API\Storage.lua:136: attempt to index field 'MetaData' (a nil value) appears right after importing a macro.

The Error

Message: Interface\AddOns\GSE\API\Storage.lua:136: attempt to index field 'MetaData' (a nil value)
Time: Thu Jun 17 07:09:14 2021
Count: 1
Stack: Interface\AddOns\GSE\API\Storage.lua:136: attempt to index field 'MetaData' (a nil value)
[string "=[C]"]: ?
[string "@Interface\AddOns\GSE\API\Storage.lua"]:136: in function `OOCAddSequenceToCollection'
[string "@Interface\AddOns\GSE\API\Events.lua"]:455: in function `?'
[string "@Interface\AddOns\Details\Libs\AceTimer-3.0\AceTimer-3.0.lua"]:55: in function <...ce\AddOns\Details\Libs\AceTimer-3.0\AceTimer-3.0.lua:50>

Locals: 

Additional context
I tried to reproduce this error #850 by copying the SLG-MM-ARCANE macro from this link but I got another error right after importing a first macro.

To Reproduce

1. Go to this link
2. Copy the SLG-MM-ARCANE macro into clipboard
3. In GSE 3.0.0 beta 5, click on the Import button and paste the macro
4. See error

Expected behavior
No error after imporing a macro from a website.

Screenshots

Desktop
OS: Windows 10 64bits pro
Hardware: nvidia GTX 1070 8GB - driver: 466.47

Game Version
World of Warcraft Shadowlands version 9.0.5.38556 (french language)

GSE Version
Version: 3.0.0 beta 5

This was fixed by #859 This change is on Curse as 3.0.0-beta-5-1-g9790015

You are importing a GSE2 Macro. The import wasn't checking if it was a GSE2 macro but expecting a GSE3 macro.