empty cells in a row in a table - how can I hide them

I have a table that may have empty cells in a row, how can I hide them?  
Below is an example of my code.  I have stripped out all attributes thinking
that maybe something is causing the rows not to hide.  
I am very new at this stuff, so any comments is much appreciated.

Thanks much,
jlr

CODE:

   <fo:table-row  >
                   <fo:table-cell  border="solid black 0.5px" empty-cells="hide">
                        <fo:block >
                            <xsl:value-of select="header/column9"/>
                        </fo:block>                  
                  </fo:table-cell>
                  <fo:table-cell  border="solid black 0.5px" empty-cells="hide">
                        <fo:block >
                            <xsl:value-of select="header/column10"/>
                        </fo:block>                      
                  </fo:table-cell>                  
                   <fo:table-cell border="solid black 0.5px" empty-cells="hide">
                        <fo:block >
                            <xsl:value-of select="header/column11"/>
                        </fo:block>                      
                  </fo:table-cell>
                  <fo:table-cell border="solid black 0.5px" empty-cells="hide">
                        <fo:block>
                            <xsl:value-of select="header/column12"/>
                        </fo:block>                    
                  </fo:table-cell>                
               </fo:table-row>