Handle endpoint name nullability in constructor

Throws an IllegalArgumentException when the endpoint name passed into
the constructor is null. This will help prevent the error from being
invoked later down the line and instead throws it at the first sign
of detection.

Fixes: 286310499
Test: atest TelecomUnitTests
Change-Id: Ic128d0e3577591d54cf9c4309844e4580af220c1