Question: Calculating Weyl tensor from a metric

MY CODE:
 

with(Physics);
Setup(mathematicalnotation = true);
Setup(Coordinatesystem = (X = [x, y, z, t]), metric = 4*dx*dt-dy^2-dz^2+4*u*(dt^2));
    * Partial match of  'Coordinatesystem' against keyword 

       'coordinatesystems'
    Systems of spacetime Coordinates are: (Xequals(x,y,z,t))
[coordinatesystems = {X}, 

  metric = {(1, 4) = 2, (2, 2) = -1, (3, 3) = -1, (4, 4) = 4 u}]
g_[];      (here g is diplayed in matrix form)

Weyl[alpha, beta, mu, nu, nonzero];
            Physics:-Weyl[alpha, beta, mu, nu] = {}

So basically i'm trying to find the nonzero components of the weyl tensor which returns the empty set, i.e the weyl tensor apparently equals zero but I know this is not the case, can anyone see if I have input something wrong? Thanks in advance

g_[] in matrix form is 
0 0 0 2
0 -1 0 0
0 0 -1 0
2 0 0 4u

UPDATE: u is a function of all varibles and I have not considered this which might be causing the problem