Rails: No connection pool for PublicActivity::ORM::ActiveRecord::Activity

Question

I'm trying to upgrade an existing project from Ruby 2.3 to Ruby 2.6

Everything was working fine until I received the following error on running rake db:create

rake aborted!
ActiveRecord::ConnectionNotEstablished: No connection pool for PublicActivity::ORM::ActiveRecord::Activity
/home/user/project/engines/admin/lib/admin/activity_extension.rb:10:in `<module:Admin>'
/home/user/project/engines/admin/lib/admin/activity_extension.rb:1:in `<top (required)>'
/home/user/project/engines/admin/lib/admin/engine.rb:8:in `<top (required)>'
/home/user/project/engines/admin/lib/admin.rb:1:in `require'
/home/user/project/engines/admin/lib/admin.rb:1:in `<top (required)>'
/home/user/project/config/application.rb:17:in `<top (required)>'
/home/user/project/Rakefile:4:in `<top (required)>'

I'm using postgresql as database and this is the database.yml file -

default: &default
  adapter: postgresql
  encoding: unicode
  username: -------
  password: -------
  host: localhost
  port: 5432
  pool: 5

development:
  <<: *default
  database: mydbName

Is anyone having any idea why I'm getting this error?

Any kind of help would be greately appreciated!