title: The XML Tag doesn't appear when the Value is Null in the Query in Oracle
body: <p>How can I retrieve the XML tags when the field is NULL? This is the Query:</p>
  
  <pre><code>  SELECT XMLElement("FlowerSeeds" , XMLAttributes('http://euroconsumers.org/' as "xmlns")
             , xmlforest(
                         d.cli_pre_l "Name"
                         , d.cli_nom_l "FirstName"
                         , COALESCE(d.cli_gsm_c, NULL) "Phone"                       
                         , d.cli_eml_c "Email"
                         , 
                            xmlforest (
                                             d.cli_rue_l "Street"
                                             , d.CLI_RUE_NUM_L "StreetNumber"
                                             , d.cli_cpo_c "PostalCode"
                                             , d.cli_loc_l "City"
                                             , null as "District"
                             ) "DeliveryAddress"
                        )
                    ).getclobval()
    FROM TA_MAIN.clients d
   WHERE d.cli_id_s = 2504217
  </code></pre>
  
  <p>I have a problem when some field is NULL, the tag of XML is not generated.</p>
  
  <p>For example: When the value of Phone or Email is NULL, the XML tag is not generated. How can I create XML tag even when the value is null?</p>
  
  <p>Like this:</p>
  
  <pre><code>&lt;FlowerSeeds xmlns="http://euroconsumers.org/"&gt;
      &lt;Name&gt;SYLVIA&lt;/Name&gt;
      &lt;FirstName&gt;DEL&lt;/FirstName&gt;
      &lt;DeliveryAddress&gt;
          &lt;Street&gt;AVENUE DE ROG 135&lt;/Street&gt;
          &lt;StreetNumber&gt;135&lt;/StreetNumber&gt;
          &lt;PostalCode&gt;1285&lt;/PostalCode&gt;
          &lt;City&gt;WOLUWE&lt;/City&gt;
      &lt;/DeliveryAddress&gt;
  &lt;/FlowerSeeds&gt;
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/ptx4u.png" alt="Result"></p>