Merge two trees creating a Index reflecting the result of the merge.
| this |
a Repository. |
| ancestor_tree |
the common ancestor between the trees, or null. |
| our_tree |
the tree that reflects the destination tree. |
| their_tree |
the tree that reflects the source tree. |
| merge_options |
the merge options. |
|
a new Index or null if an error occurred. |