Web terminal not working with group cluster

Summary

Kubernetes web terminal cannot be accessed if the cluster is a group level cluster

Steps to reproduce

1. Add a Kubernetes cluster to a group
2. Deploy to Kubernetes in a project inside that group
3. Go to the project page > Operations > Environments

What is the current bug behavior?

The Terminal button in the environments list is disabled:

The terminal button in the environment detail view is active, but the terminal itself shows "Connection failure":

What is the expected correct behavior?

Web terminals should work exactly the same like when the cluster is added to the project directly.

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:         Ubuntu 16.04
Current User:   git
Using RVM:      no
Ruby Version:   2.5.3p105
Gem Version:    2.7.6
Bundler Version:1.17.3
Rake Version:   12.3.2
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.5
Go Version:     unknown

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab subtasks ...
Checking GitLab Shell ...
GitLab Shell: ... GitLab Shell version >= 9.0.0 ? ... OK (9.0.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Gitaly ...
Gitaly: ... default ... OK
Checking Gitaly ... Finished
Checking Sidekiq ...
Sidekiq: ... Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Checking Incoming Email ...
Incoming Email: ... Reply by email is disabled in config/gitlab.yml
Checking Incoming Email ... Finished
Checking LDAP ...
LDAP: ... LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab App ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
5/2 ... yes
4/3 ... yes
5/8 ... yes
18/10 ... yes
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98/173 ... yes
39/175 ... yes
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51/180 ... yes
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113/182 ... yes
18/183 ... yes
5/184 ... yes
113/185 ... yes
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98/187 ... yes
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18/246 ... yes
4/247 ... yes
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77/251 ... yes
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158/254 ... yes
39/255 ... yes
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59/257 ... yes
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18/265 ... yes
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159/269 ... yes
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77/271 ... yes
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162/277 ... yes
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39/304 ... yes
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59/324 ... yes
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177/327 ... yes
5/329 ... yes
175/330 ... yes
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179/333 ... yes
131/334 ... yes
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175/336 ... yes
51/337 ... yes
51/341 ... yes
113/342 ... yes
2/343 ... yes
99/344 ... yes
51/345 ... yes
18/346 ... yes
5/347 ... yes
2/348 ... yes
2/349 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.5.3)
Git version >= 2.18.0 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 93
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished

Possible fixes

I traced down the problem to this line, where project is falsy so the function returns immediately.