Fix NPE on DatadogServerRequestResponseFlowWrapper

[dtremper]

What Does This Do

solves #9017

Motivation

Additional Notes

Contributor Checklist

• Format the title according the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any usefull labels
• Don't use close, fix or any linking keywords when referencing an issue.
  Use solves instead, and assign the PR milestone to the issue
• Update the CODEOWNERS file on source file addition, move, or deletion
• Update the public documentation in case of new configuration flag or behavior

Jira ticket: [PROJ-IDENT]

[mcculls]

Hi @dtremper - thanks for the patch, there are a couple more fixes needed since this also affects the pekko-http integration: #9019 should address this

[mcculls]

Resolved by #9019