Suppress warning "Comparable#== will no more rescue exceptions of #<=> in the next release."

Hi, thank you for your nice gem.

Unfortunately, `Comparable#==` will no more rescue exception in future release.
Thus `timeuuid == nil` raises undefined method exception.
This warning shows in ruby 2.2.0-preview1.

I try to write patch for this problem.
How about this?

see also: https://bugs.ruby-lang.org/issues/7688