Evaluation Error: Error while evaluating a Function Call, undefined method `length' for nil:NilClass

Puppet Version: puppet-agent-6.26
Puppet Server Version: puppetserver-6.18
OS Name/Version: CentOS 7

After executing the command of puppet agent -t we get the following error:

Info: Using environment 'production'
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Retrieving locales
Info: Loading facts
Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Error while evaluating a Function Call, undefined method `length' for nil:NilClass (file: /etc/puppetlabs/code/modules/yum/manifests/init.pp, line: 202, column: 20) on node XXX
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run

We change the configuration of the init.pp with a solution that we encounter somewhere, and was to change this code:

$_pc_cmd = delete_undef_values([

    '/usr/bin/package-cleanup',

    '--oldkernels',

    "--count=${_real_installonly_limit}",

    '-y',

    $keep_kernel_devel ? {

      true    => '--keepdevel',

      default => undef,

    },

  ]) 

to this other one:

$_pc_cmd = [

    '/usr/bin/package-cleanup',

    '--oldkernels',

    "--count=${_real_installonly_limit}",

    '-y',

    $keep_kernel_devel ? {

      true    => '--keepdevel',

      default => undef,

    },

  ].filter |$val| { $val =~ NotUndef } 

There is a way of solving this issue whithout making any changes on the code?

Desired Behavior: No puppet errors

Actual Behavior: Execution getting errors