Bench update error (develop branch)

I’m getting another error with a bench update, related to the length of a key:

Patching sites...
Migrating ##site##
Executing execute:frappe.reload_doc('core', 'doctype', 'docperm') #2018-05-29 in ##site## (9ed8d899d738b1d3)
Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/erp/frappe-bench/apps/frappe/frappe/utils/bench_helper.py", line 97, in <module>
    main()
  File "/home/erp/frappe-bench/apps/frappe/frappe/utils/bench_helper.py", line 18, in main
    click.Group(commands=commands)(prog_name='bench')
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/home/erp/frappe-bench/env/local/lib/python2.7/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/peter/frappe-bench/apps/frappe/frappe/commands/__init__.py", line 25, in _func
    ret = f(frappe._dict(ctx.obj), *args, **kwargs)
  File "/home/erp/frappe-bench/apps/frappe/frappe/commands/site.py", line 222, in migrate
    migrate(context.verbose, rebuild_website=rebuild_website)
  File "/home/erp/frappe-bench/apps/frappe/frappe/migrate.py", line 39, in migrate
    frappe.modules.patch_handler.run_all()
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/patch_handler.py", line 29, in run_all
    if not run_single(patchmodule = patch):
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/patch_handler.py", line 63, in run_single
    return execute_patch(patchmodule, method, methodargs)
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/patch_handler.py", line 81, in execute_patch
    exec(patchmodule.split("execute:")[1],globals())
  File "<string>", line 1, in <module>
  File "/home/erp/frappe-bench/apps/frappe/frappe/__init__.py", line 698, in reload_doc
    return frappe.modules.reload_doc(module, dt, dn, force=force, reset_permissions=reset_permissions)
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/utils.py", line 155, in reload_doc
    return import_files(module, dt, dn, force=force, reset_permissions=reset_permissions)
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/import_file.py", line 19, in import_files
    reset_permissions=reset_permissions)
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/import_file.py", line 24, in import_file
    ret = import_file_by_path(path, force, pre_process=pre_process, reset_permissions=reset_permissions)
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/import_file.py", line 58, in import_file_by_path
    ignore_version=ignore_version, reset_permissions=reset_permissions)
  File "/home/erp/frappe-bench/apps/frappe/frappe/modules/import_file.py", line 132, in import_doc
    doc.insert()
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 249, in insert
    self.run_post_save_methods()
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 898, in run_post_save_methods
    self.run_method("on_update")
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 765, in run_method
    out = Document.hook(fn)(self, *args, **kwargs)
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 1040, in composer
    return composed(self, method, *args, **kwargs)
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 1023, in runner
    add_to_return_value(self, fn(self, *args, **kwargs))
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 759, in <lambda>
    fn = lambda self, *args, **kwargs: getattr(self, method)(*args, **kwargs)
  File "/home/erp/frappe-bench/apps/frappe/frappe/core/doctype/doctype/doctype.py", line 219, in on_update
    updatedb(self.name, self)
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/db_schema.py", line 77, in updatedb
    tab.sync()
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/db_schema.py", line 159, in sync
    self.alter()
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/db_schema.py", line 359, in alter
    raise e
pymysql.err.InternalError: (1071, u'Specified key was too long; max key length is 767 bytes')

Any tips? I understand that this is a problem with a patch, but I can’t find any information in the output to indicate which patch is causing the problem.

Thanks in advance!