merge.xts segfault with empty xts object and more than 1 non-xts object

[joshuaulrich]

This appears to be caused by mergeXts attempting to set dimnames on a vector. All commands below cause a segfault. Thanks for Jeffrey Mazar for the reproducible example.

merge(xts(), 0, xts())
merge(xts(), xts(), 0)
merge(xts(), xts(), "")

[joshuaulrich]

A couple more observations:

1. merge(xts(), 1, 1) also crashes. Seems like anything with an empty xts object will fail, except the 2-way merge: merge(xts(), 1).
2. If the second argument (y) passed to do_merge_xts is not an xts object, it is converted to xts via the equivalent of: y_xts <- try.xts(y, length.out = length(index(x)), error = xts:::.merge.xts.scalar). In the case of merge(xts(), 0, xts()), y = 0 and length.out = 0L. So y_xts is a matrix with no rows and 1 column.
3. The expected behavior of merge(xts(), 1, 1) is the same as merge(merge(xts(), 1), 1).