Replace usage of require.Nil/NotNil with require.Error/NoError when using errors for the web package

Description

None

QA Test Steps

No testing required.
No testing required.
No testing required.

Done

Mana

None

Assignee

Jesús Espino

QA Assignee

None

Reporter

Jesús Espino

Epic Link

None

Fix versions

Mattermost Team

Server

Sprint

None

Labels

None

QA Testing Areas

None

GitHub Issue

None

Components

None