colVars for dgeMatrix

I am working with large sparse matrices that, after some operations, can return non-sparse matrices of class `dgeMatrix`.

I must be missing something here, but when I try to get colVars for a `dgeMatrix`, I get

```
Error in MatrixGenerics:::.load_next_suggested_package_to_search(x) :
Failed to find a colVars() method for dgeMatrix objects.
```

even though `colMeans2` works just fine.

Here is some (hopefully) reproducible code:

```
m <- Matrix(nrow = 3, ncol = 6, data = rnorm(18), sparse = FALSE)
sparseMatrixStats::colVars(m)
```

PS: `matrixStats::colVars(m)` returns

```
Error in matrixStats::colVars(m) :
Argument 'x' must be a matrix or a vector.
```

and calling `as.matrix` prior to `matrixStats::colVars` is very slow on larger matrices.

Any help would be much appreciated.