fix: plan-parity on no-change (#447)

Signed-off-by: Rishav Dhar <19497993+rdhar@users.noreply.github.com>

Author: rdhar

README.md

@@ -140,12 +140,12 @@ Before the workflow uploads the plan file as an artifact, it can be encrypted-at
 In order to decrypt the plan file locally, use the following commands after downloading the artifact (adding a whitespace before `openssl` to prevent recording the command in shell history):
 
 ```fish
-unzip <tf.plan>
+unzip <tfplan.zip>
 openssl enc -d -aes-256-ctr -pbkdf2 -salt \
-  -in <tf.plan> \
-  -out tf.plan.decrypted \
+  -in   tfplan.encrypted \
+  -out  tfplan.decrypted \
   -pass pass:"<passphrase>"
-<tf.tool> show tf.plan.decrypted
+<tf.tool> show tfplan.decrypted
 ```
 
 </br>

action.yml

@@ -251,8 +251,8 @@ runs:
         # Both plan files are normalized by sorting JSON keys, removing timestamps and ${{ steps.arg.outputs.arg-detailed-exitcode }} to avoid false-positives.
         if [[ -n "$PLAN_FILE" ]]; then mv --force --verbose "$PLAN_FILE" "$path" 2>/dev/null; fi
         ${{ inputs.tool }}${{ steps.arg.outputs.arg-chdir }} plan${{ steps.arg.outputs.arg-destroy }}${{ steps.arg.outputs.arg-var-file }}${{ steps.arg.outputs.arg-var }}${{ steps.arg.outputs.arg-compact-warnings }}${{ steps.arg.outputs.arg-concise }}${{ steps.arg.outputs.arg-generate-config-out }}${{ steps.arg.outputs.arg-lock-timeout }}${{ steps.arg.outputs.arg-lock }}${{ steps.arg.outputs.arg-parallelism }}${{ steps.arg.outputs.arg-refresh-only }}${{ steps.arg.outputs.arg-refresh }}${{ steps.arg.outputs.arg-replace }}${{ steps.arg.outputs.arg-target }} -out=tfplan.parity
-        ${{ inputs.tool }}${{ steps.arg.outputs.arg-chdir }} show -json tfplan.parity | jq --sort-keys '[.resource_changes[] | select(.change.actions != ["no-op"])]' > tfplan.new
-        ${{ inputs.tool }}${{ steps.arg.outputs.arg-chdir }} show -json tfplan | jq --sort-keys '[.resource_changes[] | select(.change.actions != ["no-op"])]' > tfplan.old
+        ${{ inputs.tool }}${{ steps.arg.outputs.arg-chdir }} show -json tfplan.parity | jq --sort-keys '[(.resource_changes? // [])[] | select(.change.actions != ["no-op"])]' > tfplan.new
+        ${{ inputs.tool }}${{ steps.arg.outputs.arg-chdir }} show -json tfplan | jq --sort-keys '[(.resource_changes? // [])[] | select(.change.actions != ["no-op"])]' > tfplan.old
         # If both plan files are identical, then replace the old plan file with the new one to prevent avoidable stale apply.
         diff tfplan.new tfplan.old && mv --force --verbose "${{ format('{0}{1}tfplan.parity', inputs.arg-chdir || inputs.working-directory, (inputs.arg-chdir || inputs.working-directory) && '/' || '') }}" "${{ format('{0}{1}tfplan', inputs.arg-chdir || inputs.working-directory, (inputs.arg-chdir || inputs.working-directory) && '/' || '') }}"
         rm --force tfplan.new tfplan.old "${{ format('{0}{1}tfplan.parity', inputs.arg-chdir || inputs.working-directory, (inputs.arg-chdir || inputs.working-directory) && '/' || '') }}"