lib/ews/soap/builders/ews_builder.rb
def additional_properties!(addprops)
      @nbuild[NS_EWS_TYPES].AdditionalProperties {
        addprops.each_pair {|k,v|
          dispatch_field_uri!({k => v}, NS_EWS_TYPES)
        }
      }
    end
def additional_properties!(addprops)
      @nbuild[NS_EWS_TYPES].AdditionalProperties {
        addprops.each_pair {|k,v|
          dispatch_field_uri!({k => v}, NS_EWS_TYPES)
        }
      }
    end
Build the AdditionalProperties element
 @see http://msdn.microsoft.com/en-us/library/aa563810.aspx