How do I find this particular boundary element for solving differential equations

Hello, I'm trying to find the solution for this equation

(d^2T/dr^2) + (1/r)*(dT/dr) + S= 0;

they give us S=20; T(r=1)=1 and (dT/dr)=0 when r=0

The problem is if you replace the derivatives by zero you get S=0, each is not true.

At the moment I have T(r=0)=20 because it makes the most sense for me but i dont know.

I have to solve this equation through matrices in matlab but to do so i need two boundary values. my code is

S=20; dr=0.01; r=0:dr:1; n=length(r);

%boundary conditions cfe=20; cfd=1;

M=zeros(n,n); y=zeros(n,1);

A=r-dr/2; %after

B=r+dr/2; %before

C=-2*r; %center

J=-S*dr^2;%right side of equation

% ptos interiores

for i=2:n-1

M(i,i)=C(i);

M(i,i-1)=B(i);

M(i,i+1)=A(i);

y(i)=J*r(i);
end
%Primeiro valor
M(1,1)=1;M(1,2)=0; 
M(n,n)=1;M(n,n-1)=0;
y(1)=cfe;y(n)=cfd;

% T=y/M; T=M\y;

 figure(1)
 plot(r,T,'r')

 xlabel('Raio'); ylabel('K');
 title('Temperatura em função do raio');

 grid on