Question: why simplify((),size) returns size?

Is this an expected behaviour for simplify/size? 

I was simplifying a result from pdsolve, but did not check that the solution was null or () before calling simplify.

It turns out that  simplify((),size)  returns size for this. I find this is very strange.

I would have expected it to return ().

I can fix this by checking that sol is not null before calling simplify ofcourse. But the question is, why does simplify((),size) return size? What is the logic for this? From help:

The simplify(expr, size) calling sequence is used to attempt simplifying the expression size, performing only collections and simple decomposition of fractional powers in the coefficients - sometimes taking advantage of linear factors when they exist. No other mathematical simplifications of the expression or its subexpressions is performed. These operations, while simple and with low computational cost, may remarkably structure the expression and reduce its size.
 

is it possible what happens is this: becuase "sol" was null, the call simplify(sol,size) has actually become simplify(size) and the result is size.  So because the first slot in the call was (), it was ignored during the call and the first parameter became size insteal of sol?

Maple 2019 on windows 10.