Internal partition and external glazing

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When doing a refit of an workplace, how do new inside partitions hook up with exterior glazing? The prevailing partitions hook up with a mullion however what if there is no such thing as a mullion the place the brand new partition must go? In the actual world would they refit the outside glazing and work in a brand new mullion or is there an easier resolution? I’ve a picture to higher clarify however don't know how one can put up. Thanks prematurely, a grateful pupil.