undefined method 'pool' for Sidetiq::Supervisor:Class

Question

I am working on a rails application. On running command bundle exec sidekiq I am getting the following error -

undefined method `pool' for Sidetiq::Supervisor:Class
/.rvm/gems/ruby-2.6.3/gems/sidetiq-0.6.0/lib/sidetiq/supervisor.rb:12:in `<class:Supervisor>'
/.rvm/gems/ruby-2.6.3/gems/sidetiq-0.6.0/lib/sidetiq/supervisor.rb:2:in `<module:Sidetiq>'
/.rvm/gems/ruby-2.6.3/gems/sidetiq-0.6.0/lib/sidetiq/supervisor.rb:1:in `<top (required)>'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `require'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `block in require'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:240:in `load_dependency'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `require'
/.rvm/gems/ruby-2.6.3/gems/sidetiq-0.6.0/lib/sidetiq.rb:32:in `<top (required)>'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `require'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `block in require'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:240:in `load_dependency'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `require'
/application/engines/common/lib/common/engine.rb:17:in `<top (required)>'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `require'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `block in require'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:240:in `load_dependency'
/.rvm/gems/ruby-2.6.3/gems/activesupport-4.2.11.3/lib/active_support/dependencies.rb:274:in `require'
/application/engines/common/lib/common.rb:1:in `<top (required)>'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler/runtime.rb:66:in `require'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler/runtime.rb:66:in `block (2 levels) in require'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler/runtime.rb:61:in `each'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler/runtime.rb:61:in `block in require'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler/runtime.rb:50:in `each'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler/runtime.rb:50:in `require'
/.rvm/gems/ruby-2.6.3/gems/bundler-2.2.15/lib/bundler.rb:173:in `require'
/application/config/application.rb:17:in `<top (required)>'
/.rvm/gems/ruby-2.6.3/gems/sidekiq-4.1.4/lib/sidekiq/cli.rb:232:in `require'
/.rvm/gems/ruby-2.6.3/gems/sidekiq-4.1.4/lib/sidekiq/cli.rb:232:in `boot_system'
/.rvm/gems/ruby-2.6.3/gems/sidekiq-4.1.4/lib/sidekiq/cli.rb:50:in `run'
/.rvm/gems/ruby-2.6.3/gems/sidekiq-4.1.4/bin/sidekiq:12:in `<top (required)>'
/.rvm/gems/ruby-2.6.3/bin/sidekiq:23:in `load'
/.rvm/gems/ruby-2.6.3/bin/sidekiq:23:in `<main>'
/.rvm/gems/ruby-2.6.3/bin/ruby_executable_hooks:22:in `eval'
/.rvm/gems/ruby-2.6.3/bin/ruby_executable_hooks:22:in `<main>'

It is pointing towards this piece of code in the first line of trace -

if Sidekiq.server?
      if handler_pool_size = Sidetiq.config.handler_pool_size
        pool Sidetiq::Actor::Handler,
             as: :sidetiq_handler,
             size: handler_pool_size
      else
        # Use Celluloid's CPU-based default.
        pool Sidetiq::Actor::Handler,
             as: :sidetiq_handler
      end
    end

I am not able to find out the root of this error.

Is there any gem that I am missing?

Does anyone has any idea how to resolve this issue?

Please help! Its important!