🐛 Source HubSpot: Fix empty string inside number / float datatype

[bazarnov]

What

#5293 - Source Hubspot fails in normalization step

How

• added additional field_value verification for an empty string to api.py, if so - set the field_value to be zero, instead of empty string.
• edited test_field_type_converting.py unit-test to simulate the issue of empty string inside numeric (float) type

NOTE:
This fix potentially could resolve the issue with Bad Double Value when using this connector along with Destination BigQuery for data replication. As far as BigQuery does not accept simple null values, and could not accept empty strings as numeric values, it requires additional data preprocessing before inject the data into the table.

Pre-merge Checklist

Updating a connector

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• Unit & integration tests added and passing. Community members, please provide proof of success locally e.g: screenshot or copy-paste unit, integration, and acceptance test output. To run acceptance tests for a Python connector, follow instructions in the README. For java connectors run ./gradlew :airbyte-integrations:connectors:<name>:integrationTest.
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• Documentation updated
  • Connector's README.md
  • Changelog updated in docs/integrations/<source or destination>/<name>.md including changelog. See changelog example
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Airbyter

If this is a community PR, the Airbyte engineer reviewing this PR is responsible for the below items.

• Create a non-forked branch based on this PR and test the below items on it
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• /test connector=connectors/<name> command is passing.
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[bazarnov]

/test connector=connectors/source-hubspot

🕑 connectors/source-hubspot https://github.com/airbytehq/airbyte/actions/runs/1119528170
✅ connectors/source-hubspot https://github.com/airbytehq/airbyte/actions/runs/1119528170

[bazarnov]

/test connector=connectors/source-hubspot

🕑 connectors/source-hubspot https://github.com/airbytehq/airbyte/actions/runs/1124238148
✅ connectors/source-hubspot https://github.com/airbytehq/airbyte/actions/runs/1124238148

[bazarnov]

/publish connector=connectors/source-hubspot

🕑 connectors/source-hubspot https://github.com/airbytehq/airbyte/actions/runs/1124341394
✅ connectors/source-hubspot https://github.com/airbytehq/airbyte/actions/runs/1124341394