def _sanitize_value(key, value)
      case value
      when String
        value.dup.freeze
      when Symbol, Integer, Float, NilClass, TrueClass, FalseClass
        value
      when Array
        _sanitize_array(key, value)
      when Hash
        _sanitize_params(value)
      else
        raise Errors::UnsafeValueError.new(key, value)
      end
    end
def _sanitize_value(key, value)
      case value
      when String
        value.dup.freeze
      when Symbol, Integer, Float, NilClass, TrueClass, FalseClass
        value
      when Array
        _sanitize_array(key, value)
      when Hash
        _sanitize_params(value)
      else
        raise Errors::UnsafeValueError.new(key, value)
      end
    end
Sanitize an individual value.