Empty transaction_id

REQUEST :
<methodCall>
 <methodName>saveEvent</methodName>
 <params>
  <genie>
   <int>1</int>
  </genie>
  <school_id>
   <int>1</int>
  </school_id>
  <g5mid>
   <int>054103087117116119114109086116113050107118103089098117118099100122081098043048075056098053088118112101115050</int>
  </g5mid>
  <transaction_id>
   <string></string>
  </transaction_id>
  <action>
   <string>save</string>
  </action>
  <user_choice>
   <int></int>
  </user_choice>
  <event_id>
   <int></int>
  </event_id>
  <type>
   <string>nonconference</string>
  </type>
  <event_type>
   <string>25013</string>
  </event_type>
  <activity_id>
   <int>19124</int>
  </activity_id>
  <date>
   <string>2018-02-28</string>
  </date>
  <time_from>
   <string>15:00:00</string>
  </time_from>
  <time_to>
   <string>16:00:00</string>
  </time_to>
  <location_id>
   <int>19651</int>
  </location_id>
  <location_detail_id>
   <array>2182</array>
  </location_detail_id>
  <location_public_view>
   <array>2182
   </array>
  </location_public_view>
  <status>
   <int>0</int>
  </status>
  <home_school>
   <int>1</int>
  </home_school>
  <away_schools>
   <int>8</int>
  </away_schools>
  <worksheet>
   <int>10263</int>
  </worksheet>
  <setup_notes>
   <string></string>
  </setup_notes>
  <number_of_attendees>
   <int></int>
  </number_of_attendees>
  <comment>
   <string></string>
  </comment>
  <comment1>
   <string></string>
  </comment1>
  <setup_start>
   <string></string>
  </setup_start>
  <setup_end>
   <string></string>
  </setup_end>
  <bus_leaves>
   <string></string>
  </bus_leaves>
  <bus_dismiss>
   <string></string>
  </bus_dismiss>
  <bus_return>
   <string></string>
  </bus_return>
  <bus_notes>
   <string></string>
  </bus_notes>
  <bus_company>
   <string>
   </string>
  </bus_company>
  <dont_show_bus_time>
   <string></string>
  </dont_show_bus_time>
  <external_id>
   <int></int>
  </external_id>
  <external_type>
   <string></string>
  </external_type>
 </params>
</methodCall>

RESPONSE :
<methodResponse>
    <params>
        <response_code>
            <int>1</int>
        </response_code>
        <event_id>
            <int>206411</int>
        </event_id>
        <notify_list>
            <array>cherrylyn.remolador@dwebsite.net, precious@dwebsite.net,navalprecious5@gmail.com,dwctsr02@gmail.com,navalprecious5@gmail.com,saulius@dwebsite.net,ulinha89@gmail.com</array>
        </notify_list>
    </params>
</methodResponse>