Creating a custom distribution gumbel in Distribution Fitting tool by setting k in the Generalized Extreme Value function to 0

I want to create a Gumbel distribution (Generalized Extreme Value Type I, which is when k=0) in the distribution fitting toolbox. If I use the Generalized Extreme Value function, the k-value is set to what Matlab feel is appropriate. However, I want k to always be 0, since I always want to use the Gumbel function. I tried looking for a k value in LaplaceDistribution.m(the file that one should edit to create a custom distribution) but couldn't find anything. Do you have any idea how to edit this file to set k to 0, or should I do it in some other way?

I looked at creating the function outside of the toolbox and then I think it should look like this, with mu and sigma being what the distribution fitting toolbox decides.

gevpdf(x,0,sigma,mu)