Solve nonlinear numerical differential equations with several variables?

Dear Wolfram community,

I have a nonlinear system with two variables. For Example:

Clear["Global`*"]
system = {
   D[a[t, x], t] == a[t, x] + b[t, x], 
   D[b[t, x], x] == a[t, x] b[t, x],
   a[t, 0] == 0.5, b[0, x] == 1};
solution = NDSolve[system, {a, b}, {t, 0, 10}, {x, 0, 10}]

and get as an error massgae:

NDSolve::femnonlinear: Nonlinear coefficients are not supported in this version of NDSolve..

What is my problem and my miss understanding?

Thank for your help.

What version are you running? It works on V12.

With version Mathematica 12.0 works fine.

I use the version Mathematica 11.3.

Thank for your help.

Now, its work with Mathematica 12.0