[Backport 2.12] Bug Fix: Fix for rag processor throwing NPE

[pyek-bot]

PS: Please add backport label to 2.11

(cherry picked from commit 8b5b38e)

Description

Backporting RAG NPE fix to 2.12

Related Issues

Resolves #2983

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[opensearch-trigger-bot]

The backport to 2.11 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.11 2.11
# Navigate to the new working tree
cd .worktrees/backport-2.11
# Create a new branch
git switch --create backport/backport-3089-to-2.11
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 45e93d7057e72d96e9193b02d052e51e086416e2
# Push it to GitHub
git push --set-upstream origin backport/backport-3089-to-2.11
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.11

Then, create a pull request where the base branch is 2.11 and the compare/head branch is backport/backport-3089-to-2.11.