ActionView::Template::Error: undefined method `>' for nil:NilClass

https://sentry.gitlab.net/gitlab/gitlabcom/issues/671055/

NoMethodError: undefined method `>' for nil:NilClass
  merge_request.rb:1299:in `has_commits?'
    merge_request_diff && commits_count > 0
  gitlab/metrics/instrumentation.rb:161:in `block in has_commits?'
    .measure { super }
  gitlab/metrics/method_call.rb:36:in `measure'
    retval = yield
  gitlab/metrics/instrumentation.rb:161:in `has_commits?'
    .measure { super }
  merge_request.rb:1303:in `has_no_commits?'
    !has_commits?
...
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ActionView::Template::Error: undefined method `>' for nil:NilClass

ActionView::Template::Error: undefined method `>' for nil:NilClass