MATLAB: Dealing with v(end+1) when v(1) may not have been defined

I use the following kind of construction a lot

v(1) = (x+y)^2;
v(end+1) = (x^2 + 2*x*y + y^2)

etc. Sometimes v would be a vector of symbolic expressions, sometimes they are numeric.

I'd like to be able to initialize v in some way so that I could begin with

v(end+1) = (x+y)^2

and thus not treat the first element of the array in a special way.

I.e., I'd like to be able to do something like

v        = ''
v(end+1) = (x+y)^2;
v(end+1) = (x^2 + 2*x*y + y^2)

But this doesn't work. Is there a way to do this?

Thanks for any suggestions.