def to_hash arr
      return {}   if arr.nil?
      return arr  if arr.kind_of?(Hash)
      arr = [ arr.to_sym ]  unless arr.kind_of?(Array)
      ret = {}
      arr.each { |key| ret[key.to_sym] = {} }
      ret
    end
def to_hash arr
      return {}   if arr.nil?
      return arr  if arr.kind_of?(Hash)
      arr = [ arr.to_sym ]  unless arr.kind_of?(Array)
      ret = {}
      arr.each { |key| ret[key.to_sym] = {} }
      ret
    end
Normalizes `required` and `optional` fields to the form of Hash with options.
 @param [NilClass,Hash,Array, etc.] arr Something to normalize.