[GCP] [DNS logs] Don't parse rdata when it is empty

[zmoog]

Proposed commit message

Extends the pipeline script processor check to process rdata field only if it's not null and not an empty string.

A user reported pipeline errors occurring when the rdata is an empty string.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

How to test this PR locally

cd packages/gcp

$ elastic-package test pipeline -v  

2023/11/09 13:59:01 DEBUG GET https://127.0.0.1:5601/api/status
--- Test results for package: gcp - START ---
╭─────────┬────────────────────┬───────────┬──────────────────────────┬────────┬──────────────╮
│ PACKAGE │ DATA STREAM        │ TEST TYPE │ TEST NAME                │ RESULT │ TIME ELAPSED │
├─────────┼────────────────────┼───────────┼──────────────────────────┼────────┼──────────────┤
│ gcp     │ audit              │ pipeline  │ test-audit.log           │ PASS   │  15.953834ms │
│ gcp     │ audit              │ pipeline  │ test-sdh-3695.log        │ PASS   │   2.896625ms │
│ gcp     │ compute            │ pipeline  │ test-gcp-compute.json    │ PASS   │      1.758ms │
│ gcp     │ dns                │ pipeline  │ test-dns-empty-rdata.log │ PASS   │   4.668583ms │
│ gcp     │ dns                │ pipeline  │ test-dns.log             │ PASS   │  11.604458ms │
│ gcp     │ firewall           │ pipeline  │ test-firewall.log        │ PASS   │   7.663833ms │
│ gcp     │ loadbalancing_logs │ pipeline  │ test-load-balancer.log   │ PASS   │   3.258583ms │
│ gcp     │ vpcflow            │ pipeline  │ test-vpcflow.log         │ PASS   │  60.242458ms │
╰─────────┴────────────────────┴───────────┴──────────────────────────┴────────┴──────────────╯
--- Test results for package: gcp - END   ---
Done

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Build stats

• Start Time: 2023-11-21T04:57:06.579+0000

• Duration: 19 min 57 sec

Test stats 🧪

Test	Results
Failed	0
Passed	69
Skipped	0
Total	69

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (6/6)	💚
Files	100.0% (6/6)	💚
Classes	100.0% (6/6)	💚
Methods	87.826% (101/115)	👎 -4.274
Lines	95.124% (1502/1579)	👍 3.559
Conditionals	100.0% (0/0)	💚

[kaiyan-sheng]

Looks good to me.

[zmoog]

Hey @efd6, do you think we should make other changes to this PR, or we're good?

[elasticmachine]

Package gcp - 2.31.2 containing this change is available at https://epr.elastic.co/search?package=gcp