Support struct field with dynamic disabled

[qianheng-aws]

Description

Support struct field with dynamic disabled

If dynamic mapping disabled, although information of type missed for the new added fields, we can still parse value from the content by itself only.

Related Issues

Resolves #3343

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• API changes companion pull request created.
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• Public documentation issue/PR created.

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[qianheng-aws]

Another issue is that we don't serialize json whose value is null.

For example:

POST {{baseUrl}}/_bulk/
Content-Type: application/x-ndjson

{"index": {"_index": "test001"}}
{"profile": {"age": 1}}
{"index": {"_index": "test001"}}
{"profile": {"address": null}}

We will currently get result for PPL source=test001:

{
  "schema": [
    {
      "name": "profile",
      "type": "struct"
    }
  ],
  "datarows": [
    [
      {
        "age": 1
      }
    ],
    [
      {}
    ]
  ],
  "total": 2,
  "size": 2
}

But will get this if configuring serializeNulls for GSON:

{
  "schema": [
    {
      "name": "profile",
      "type": "struct"
    }
  ],
  "datarows": [
    [
      {
        "age": 1
      }
    ],
    [
      {
        "address": null
      }
    ]
  ],
  "total": 2,
  "size": 2
}

Which result do we want to generate? I would prefer the latter one. Shall we fix this as well? @penghuo

[LantaoJin]

+1 for serializeNulls

[LantaoJin]

can we add some comment to explain why we parse context when field type is not present?

[LantaoJin]

Ping @penghuo @dai-chen @Swiddis