fix: ignore undefined fields signature

[lissavxo]

Related to #1047

Description

Ignore undefined fields when creating signature payload to remove the + sign in the beginning of the signature payload

Test plan

Create a POST trigger with txid, timestamp, and signature fields check if the signature payload fields does not have an extra + in the beginning

[Copilot]

Pull Request Overview

Fixes an issue where undefined, null, or empty fields were being included in signature payload generation, causing unwanted '+' signs at the beginning of the signature payload string.

• Filter out undefined, null, and empty string values before joining signature payload components
• Extract the mapping result to a variable for cleaner filtering logic

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[Copilot]

[nitpick] The filter condition can be simplified using a more concise truthy check. Consider using .filter(Boolean) or .filter(value => value) instead of explicitly checking for undefined, null, and empty string, as these are all falsy values.

Suggested change

	}).filter(value => value !== undefined && value !== null && value !== '')
	}).filter(Boolean)