EAP 7 instance is not starting with duplicate resource error (WFLYCTL0212)

Issue

• After modifying standalone.xml to configure SSL, server is not starting up and shows the following error:

ERROR [org.jboss.as.controller.management-operation] (ServerService Thread Pool -- 24) WFLYCTL0013: Operation ("add") failed - address: ([
    ("subsystem" => "undertow"),
    ("server" => "default-server"),
    ("https-listener" => "https")
]) - failure description: "WFLYCTL0212: Duplicate resource [
    (\"subsystem\" => \"undertow\"),
    (\"server\" => \"default-server\"),
    (\"https-listener\" => \"https\")
]"