if some_value
     do_something
   end

  if !some_value
     do_something
  end

In some ways, the reverse is even worse: when you write

  if some_value
    do_something
  end

  if !some_value.nil?
    do_something
  end

Somehow this has never been a problem for me in eight years and hundreds of thousands of Ruby lines--but every programmer is different, and I'd like to hear other views.

change the base case of some_value from nil to 0, nil to NullObject

change some_value from nil to some sensible default like ''

What, what, what are you doing? Who uses an empty string to mean "uninitialized"? Nil and {0, "", etc) have very different semantic meanings. How would you discriminate between the default "" and a user-submitted ""? If you mean to check whether it has changed from the default, compare it to a default constant. If you mean to check emptiness, use #empty? or #blank?. I read these kinds of explicit .nil? checks as fighting the language, and in some ways, a violation of the cultural contract in Ruby and Lisp around truth charge.

This could lead to a tri-state ifs (with true/false/nil branches).

Or you can just consider that 2-branch 'if' runs the first branch if the test expr is true and the second 'otherwise'. (So that doesn't make nil false, it just makes it non-true).

And then your interpretation and everyone else co-exists and we can all code together.

What stuff should happen when something is unexpectedly nil if you tested it for truth-ishnes? Once you have written

    if not some_value
      something with some_value
    end

  if some_value
    something with some_value
  end