code: private static void generateSelectiveToTrimEleTo(XmlElement trimEle, IntrospectedColumn introspectedColumn, String prefix, int type) {
          if (type != 3 && (introspectedColumn.isSequenceColumn() || introspectedColumn.getFullyQualifiedJavaType().isPrimitive())) {
              // if it is a sequence column, it is not optional
              // This is required for MyBatis3 because MyBatis3 parses
              // and calculates the SQL before executing the selectKey
  
              // if it is primitive, we cannot do a null check
              generateSelectiveCommColumnTo(trimEle, introspectedColumn, prefix, type);
          } else {
              XmlElement eleIf = new XmlElement("if");
              eleIf.addAttribute(new Attribute("test", introspectedColumn.getJavaProperty(prefix) + " != null"));
  
              generateSelectiveCommColumnTo(eleIf, introspectedColumn, prefix, type);
  
              trimEle.addElement(eleIf);
          }
      }
docs: 生成选择列到trim 节点
  @param trimEle
  @param introspectedColumn
  @param prefix
  @param type               1:key,2:value,3:set