Recursively replace a value `initial` by `replacement`

recursive_replace.rb

def denilize(h, initial, replacement)
  h.each_with_object({}) { |(k,v),g|
    g[k] = (Hash === v) ?  denilize(v) : v == initial ? replacement : v }
end

h = { "a"=>{ "b"=>{ "c"=>nil } } }
denilize(h) #=> { "a"=>{ "b"=>{ "c"=>"" } } }

h = { "a"=>{ "b"=>{ "c"=>nil , "d"=>3, "e"=>nil}, "f"=>nil  } }
denilize(h) #=> { "a"=>{ "b"=>{ "c"=>"" , "d"=>3, "e"=>""}, "f"=>"" } }