The following error often occurs.
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06/06 13:26:49.727 ERROR (http-37080-12:) - [general] -- Resource not found: /favicon.ico
06/06 13:26:49.728 DEBUG (http-37080-12:) - [SiteServlet timings] -- Served /favicon.ico (PUBLISHED) in 2 ms
Jun 06, 2018 1:26:49 PM com.l7tech.extension.ExtensionManagerPlugin getExtension
INFO: getExtension: authenticationHandler
Jun 06, 2018 1:26:49 PM com.l7tech.extension.ExtensionManagerPlugin a
INFO: getExtension: Gateway Authentication Plugin not started. Returning null for GatewayUserManagementHandler: authenticationHandler
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What is the meaning of this error?
Is this error a problem?
If so, could you please let me know that solution?

CA API Developer Portal - 3.1
CA API Developer Portal - 3.5

The /favicon.ico is an automatic request that browsers make when a page first loads. 
There isn't any way to stop it, however the correct favicon.ico (located at /template_images/favicon.ico)
 is successfully fetched by the browser so there is no impact to the user.

This error can be ignored.