The Origin header in HTTP requests indicates the origin (protocol, host, and port) of the initiating request. However, there are certain situations where the value of this header is set to null. Here's an explanation of the scenarios:
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Cross-Origin Redirects
When a request follows a redirect from a cross-origin domain, the browser may not have a clear origin to attach to the subsequent request. Example: Request is initiated from https://site-a.com and redirects to https://site-b.com. In some cases, after the redirection, the Origin header is set to null to indicate that the origin information is not forwarded.