Description of problem:
When kubeletArguments is set to "null" within the node-config.yaml file (which is the case for cluster upgraded from previous versions to 3.9), fluentd pod cannot start throwing the following message:

"""
-e:2:in `<main>': undefined method `[]' for nil:NilClass (NoMethodError)
"""

Version-Release number of selected component (if applicable):
OCP 3.9
image logging-fluentd-v3.9*

How reproducible:
100%

Steps to Reproduce:
1. Set "kubeletArguments: null" in node-config.yaml
2. Try to start fluentd pod

Actual results:
Pod fails to start

Expected results:
Pod should start without issues

Additional info:

The error comes from the run.sh script, from this portion of the code (not present in previous fluentd images):

------ run.sh extract -----
#NOTE: USE_CRIO variable used in generate_throttle_configs.rb as well
export USE_CRIO=false
node_config=/etc/origin/node/node-config.yaml
if [[ -f "$node_config" ]]; then
    cre=$(ruby -e "require 'yaml'; y=YAML.load_file('${node_config}')
        puts y['kubeletArguments']['container-runtime-endpoint']")
    if [[ "$cre" =~ crio ]]; then
        USE_CRIO=true
    fi
else
    echo "WARNING: Unable to check for cri-o"
fi
------ run.sh extract -----