Source: Rebecca Gowers. Plain Words (2014 ed). p. 247 Middle.
Foreword: The title instances one such use of the comma.
(6) The use of a comma to mark the end of the subject of a verb, or the beginning of the object. (See also chapter 9.1.)
It cannot be said to be always wrong to use a comma to mark the end of a composite subject, because good writers sometimes do it deliberately. For instance, one might write:
The question whether it is legitimate to use a comma to mark the end of the subject, is an arguable one.
But the comma is unnecessary; the reader does not need its help.
But am I the only one who judge such commas to help separate a lengthy subject from its verb? Otherwise I'd need reread the sentence thrice. p. 175 Top of Legal Writing in Plain English (2013 2 ed.) agrees with Gowers:
1.8. Don’t use a comma between a subject and its verb.
The use of the terms “irrebuttable presumption” and “conclusive presumption,” should be discontinued as useless and confusing.
An insurance carrier or a union or union inspector, may be held liable under traditional tort concepts for the negligent performance of such an inspection.