Boundry condition for spherical system in diffusion equation

In the diffusion equation for the spherical coordinate system (m=2), we are able to define the boundary conditions as c(b,t)=1 (considering the spherical particle with an outer radius as b and inner radius is zero (solid particle)) and dc(r,t)/dr=0 (when r tends to zero). In order to compute the above conditions in Matlab, how we are going to use the dc(r,t)/dr=0 (when r tends to zero)in the boundary condition for the = general form of boundary condition defined in the given link?:

https://in.mathworks.com/help/matlab/math/solve-pde-with-material-interface.html

In the pdpe Matlab (PDE toolbox) if we put Pl=0 and ul=0 (The link suggest us to use du/dr=0, (when r tends to zero, u is c(r,t)) as u=0 in place of Pl) then the graph will tend to converge at zero (for every curve of concentration at a particular time), whereas if du/dr=0 then u must be finite but in the above link they stated to mention u =0 (in boundary condition), how we are going to deal with it in Matlab, help me with the code