fix bug: Tags.AppendTag do not work

[elvin-du]

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added entries in PENDING.md with issue #

• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #2625 into develop will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #2625      +/-   ##
===========================================
- Coverage    58.84%   58.83%   -0.02%     
===========================================
  Files          152      152              
  Lines         9424     9420       -4     
===========================================
- Hits          5546     5542       -4     
  Misses        3508     3508              
  Partials       370      370

[ValarDragon]

Could you write a test case showing that this used to fail? I'm confused as to why this changes anything.

[elvin-du]

sorry, my mistake, I open another pr to fix the bug