fix(core): Validate values which are intentionally 0

[dana-gill]

Summary

Allow for resource mapper nodes to handle intentional 0 values.

This was especially problematic in the Postgres Insert Node when a user
wants to insert 0 as a value in a table in both Fixed and Expression
mode.

In validateValueAgainstSchema, when a resolvedValue is 0, the value
is considered invalid since in Javascript, 0 is considered a falsey
value which makes !0 is equal to true.

When we are in Expression Mode and value a 0, we hit
validateFieldType with an unparsed number. This means, the value
passed in is a string (ie: '0'). This causes validateFieldType to
be consider the value as invalid because it check the type of the value
before properly parsing the value.

Workflow for testing:

{
  "nodes": [
    {
      "parameters": {
        "assignments": {
          "assignments": [
            {
              "id": "7e8e5d58-8178-4dd8-acfd-6a438dbcb982",
              "name": "num",
              "value": 0,
              "type": "number"
            }
          ]
        },
        "options": {}
      },
      "type": "n8n-nodes-base.set",
      "typeVersion": 3.4,
      "position": [
        600,
        240
      ],
      "id": "d8ffe610-f0f1-4e7f-8aa9-dd8b6cb50c70",
      "name": "Edit Fields"
    },
    {
      "parameters": {
        "schema": {
          "__rl": true,
          "mode": "list",
          "value": "public"
        },
        "table": {
          "__rl": true,
          "value": "dummy_table",
          "mode": "list",
          "cachedResultName": "dummy_table"
        },
        "columns": {
          "mappingMode": "defineBelow",
          "value": {
            "retail_price_per_unit": "={{ parseFloat($json.num) }}"
          },
          "matchingColumns": [
            "id"
          ],
          "schema": [
            {
              "id": "id",
              "displayName": "id",
              "required": false,
              "defaultMatch": true,
              "display": true,
              "type": "number",
              "canBeUsedToMatch": true,
              "removed": true
            },
            {
              "id": "retail_price_per_unit",
              "displayName": "retail_price_per_unit",
              "required": true,
              "defaultMatch": false,
              "display": true,
              "type": "number",
              "canBeUsedToMatch": true
            }
          ],
          "ignoreTypeMismatchErrors": false,
          "attemptToConvertTypes": false,
          "convertFieldsToString": false
        },
        "options": {}
      },
      "type": "n8n-nodes-base.postgres",
      "typeVersion": 2.5,
      "position": [
        820,
        240
      ],
      "id": "9e8a2ef1-1d6b-4d62-9610-2f7faaeeaa22",
      "name": "Insert 0 with Insert w/ json (Bug)",
      "credentials": {
        "postgres": {
          "id": "UeO14x83grJWzgYI",
          "name": "dgl neon"
        }
      }
    },
    {
      "parameters": {
        "schema": {
          "__rl": true,
          "mode": "list",
          "value": "public"
        },
        "table": {
          "__rl": true,
          "value": "dummy_table",
          "mode": "list",
          "cachedResultName": "dummy_table"
        },
        "columns": {
          "mappingMode": "defineBelow",
          "value": {
            "retail_price_per_unit": 0
          },
          "matchingColumns": [
            "id"
          ],
          "schema": [
            {
              "id": "id",
              "displayName": "id",
              "required": false,
              "defaultMatch": true,
              "display": true,
              "type": "number",
              "canBeUsedToMatch": true,
              "removed": true
            },
            {
              "id": "retail_price_per_unit",
              "displayName": "retail_price_per_unit",
              "required": true,
              "defaultMatch": false,
              "display": true,
              "type": "number",
              "canBeUsedToMatch": true
            }
          ],
          "ignoreTypeMismatchErrors": false,
          "attemptToConvertTypes": false,
          "convertFieldsToString": false
        },
        "options": {}
      },
      "type": "n8n-nodes-base.postgres",
      "typeVersion": 2.5,
      "position": [
        820,
        440
      ],
      "id": "968b73c1-d174-47d2-8cd2-d7a181011699",
      "name": "Insert 0 with Insert (Bug)",
      "credentials": {
        "postgres": {
          "id": "UeO14x83grJWzgYI",
          "name": "dgl neon"
        }
      }
    }
  ],
  "connections": {
    "Edit Fields": {
      "main": [
        [
          {
            "node": "Insert 0 with Insert w/ json (Bug)",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Insert 0 with Insert w/ json (Bug)": {
      "main": [
        []
      ]
    }
  },
  "pinData": {}
}

Related Linear tickets, Github issues, and Community forum posts

Partially resolves https://linear.app/n8n/issue/NODE-2085/community-issue-postgres-node-validation-fails-with-0

Partially resolves #11939

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[netroy]

besides a minor comment, LGTM

[netroy]

I don't actually know what the correct behavior here should be, but changing this means that now we will treat nulls and empty string also differently than before. Perhaps that is okay, perhaps it's now. Maybe we need to expand the check here to block both undefined and null.