`KernelSum` and `KernelProduct` with `Vector` of `Kernel` fails

[theogf]

Right now these composites will not work if the container is not a Tuple. See

k = SqExponentialKernel()
kk = KernelSum([k, k])
kk(2, 3) # Errors

[devmotion]

From looking at the code, it seems we just forgot to add a fallback for _sum? https://github.com/JuliaGaussianProcesses/KernelFunctions.jl/blob/401d556df996558c417d9f4d5c715ab079cc4e14/src/kernels/kernelsum.jl#L46 We explicitly supports constructors and summation for KernelSum with AbstractVector, so it should work. I'm surprised there's no test for it.

[theogf]

Yes sorry I started with the title, found that the code was almost right and forgot to update.

I will edit the issue name now

[theo-brown]

Has this been fixed?

[theogf]

No the issue still seems to be there. The MWE is wrong, I will adjust it.

[theogf]

Reopening as the KernelProduct still has the issue