title: Mybatis skipping update the specific column if its parameter is null
body: <p><strong>I HAVE A FOLLOWING UPDATE QUERY IN A MAPPER</strong></p>
  
  <pre><code>&lt;update id="updTest" parameterType="TestDTO"&gt;
      &lt;![CDATA[
          UPDATE   TEST_USER
  
          SET      
                EMAIL          =  #{email, jdbcType=VARCHAR}
              , USERNAME       =  #{username, jdbcType=VARCHAR}
              , PASSWORD       =  #{password, jdbcType=VARCHAR}
              , DOMAIN         =  #{domain, jdbcType=VARCHAR}
              , COMPANY        =  #{company, jdbcType=VARCHAR}
              , DEPARTMENT     =  #{department, jdbcType=VARCHAR}
              , JOBTITLE       =  #{jobtitle, jdbcType=VARCHAR}
              , SIZE           =  #{size, jdbcType=INTEGER}
              , SEX            =  #{sex, jdbcType=VARCHAR}
              , BIRTH          =  #{birth, jdbcType=VARCHAR}
              , MOBILE         =  #{mobile, jdbcType=VARCHAR}
              , STATUS         =  #{status, jdbcType=VARCHAR}
              , AUTH_KEY       =  #{authKey, jdbcType=VARCHAR}
              , UPDATE_DATE    =  SYSDATE
              , UPDATE_ID      =  #{updateId, jdbcType=VARCHAR}
              , CREATE_DATE    =  SYSDATE
              , CREATE_ID      =  #{createId, jdbcType=VARCHAR}
              , DEL_YN         =  #{delYn, jdbcType=VARCHAR}
              , DEL_ID         =  #{delId, jdbcType=VARCHAR}
  
          WHERE   USERNAME= #{username, jdbcType=VARCHAR} 
          OR      EMAIL = #{email, jdbcType=VARCHAR}
          OR      AUTH_KEY = #{authKey, jdbcType=VARCHAR}
      ]]&gt;
  &lt;/update&gt;
  </code></pre>
  
  <p><strong>WHAT I WANT TO ACHIEVE</strong> <strong><em>is to skip updating a column if its parameter is null.</em></strong></p>
  
  <p>I have a form that users will fill in these below out.</p>
  
  <ul>
  <li>JOBTITLE</li>
  <li>SIZE</li>
  <li>MOBILE</li>
  <li>BIRTH</li>
  <li>SEX</li>
  <li>STATUS</li>
  </ul>
  
  <p>This is additional information, which comes after a successful login. But when a user fills out the form and submits it, updating process works great. </p>
  
  <p><strong>But the exisiting <code>EMAIL, USERNAME, PASSWORD</code> and others are set to <code>null</code> except for those 6 fields in the form.</strong> it drives me crazy, I always thought that Mybatis would skip updating the field if its parameter is <code>null</code>. Is there any special configuration for it?</p>