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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal">I'm trying to create a class using the class item "gst."<o:p></o:p></p>
<p class="MsoNormal">The attribute in the database can only have three values (2000, 2100, and <NULL>).<o:p></o:p></p>
<p class="MsoNormal">Unfortunately, I can't create the NULL EXPRESSION.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I've already tried the following:<o:p></o:p></p>
<p class="MsoNormal">EXPRESSION IS NULL<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">EXPRESSION "<NULL>"<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">EXPRESSION <NULL><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">EXPRESSION EMPTY<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">What is the correct syntax for this?<o:p></o:p></p>
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