So, in the snippet below, x is not initialized on all paths.

def foo
  x = 1 if bar
  p x
end

So, this requires JRuby to return nil if a local var look fails. We can get rid of those if the IR can introduce necessarily initializations on all code paths. This will simply DynamicScope var looks and also eliminate conditionals in variable retrieves (see https://github.com/jruby/jruby/blob/master/core/src/main/java/org/jruby/ir/operands/TemporaryLocalVariable.java#L48-L61)