I've just updated Mercurial to 2.7 and when I tell SourceTree to use the System Mercurial and select the correct directory, I get 'Patching Mercurial Failed":-
SourceTree requires a few small changes to Mercurial to run optimally, but applying one of these patches (hg_patch_prompting_hg1.9.diff) against your system copy failed with the error ''
SourceTree will use its internal copy of Mercurial instead.
Note: the error is empty. How do I fix this?