### Cant find matrix kernel

I have a symbolic matrix at the start and I use the determinant to find roots, ok. But when I input some solution of the determinant equation in the matrix again, sage is not able to find the kernel (null space).
Here's my atempt:

```
A=matrix([[x^2,-1.75*x,0],[-1.75*x,x^2,2.07*i*x^2+4.65*i],[0,2.07*i*x^2+-4.65*i,x^2]])
sol=solve(A.det(),x,solution_dict=True)
A.subs(x=sol[0][x]).right_kernel_matrix()
```

My output is simple:

```
[]
```