lib/ews/soap/builders/ews_builder.rb
def dispatch_field_item!(item, ns_prefix = nil)
      item.values.first[:xmlns_attribute] = ns_prefix if ns_prefix
      build_xml!(item)
    end
def dispatch_field_item!(item, ns_prefix = nil)
      item.values.first[:xmlns_attribute] = ns_prefix if ns_prefix
      build_xml!(item)
    end
Insert item, enforce xmlns attribute if prefix is present