```ruby
module Fulmar
  module Infrastructure
    module Service
      # Implements Flow commands
      class FlowService
        # @param [Fulmar::Infrastructure::Service::ShellService] shell
        # @param [Hash] config
        def initialize(shell, config)
          @remote_shell = shell
          @config = config
        end

        def cache_clear
          execute('flow:cache:flush --force')
        end

        def cache_warmup
          execute('flow:cache:warmup')
        end

        def site_export(filename = export_filename)
          execute("typo3.neos:site:export --filename \"#{filename}\"")
          filename
        end

        def site_import(filename)
          execute("./flow typo3.neos:site:import --filename \"#{filename}\"")
        end

        def execute(command)
          @remote_shell.run "FLOW_CONTEXT=\"#{@config[:neos][:environment]}\" ./flow #{command}"
        end

        protected

        def export_filename
          "export_#{Time.now.strftime('%Y-%m-%dT%H%M%S')}.xml"
        end
      end
    end
  end
end
```

Check config to provide more helpful error message
user
```ruby
module Fulmar
  module Infrastructure
    module Service
      # Implements Flow commands
      class FlowService
        # @param [Fulmar::Infrastructure::Service::ShellService] shell
        # @param [Hash] config
        def initialize(shell, config)
          @remote_shell = shell
          @config = config
          test_config
        end

        def cache_clear
          execute('flow:cache:flush --force')
        end

        def cache_warmup
          execute('flow:cache:warmup')
        end

        def site_export(filename = export_filename)
          execute("typo3.neos:site:export --filename \"#{filename}\"")
          filename
        end

        def site_import(filename)
          execute("./flow typo3.neos:site:import --filename \"#{filename}\"")
        end

        def execute(command)
          @remote_shell.run "FLOW_CONTEXT=\"#{@config[:neos][:environment]}\" ./flow #{command}"
        end

        protected

        def export_filename
          "export_#{Time.now.strftime('%Y-%m-%dT%H%M%S')}.xml"
        end

        def test_config
          fail 'Neos environment is not set.' unless @config[:neos] && @config[:neos][:environment]
        end
      end
    end
  end
end
```
assistant