Bug 195607 NPE is thrown when calling DimensionHandle:: getAbsoluteValue()
If a DimensionHandle did not set DimensionValue, NPE will thrown when calling DimensionHandle:: getAbsoluteValue().
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/CSSLengthValueHandler.java
* 50% = 12px * 50(%) / 100 = 6px
	 * 
	 * @param fontSizeValue
	 *            the absolute dimension value of font size
	 * @param relativeValue
	 *            the relative dimension value to compute
	 * @return the absolute dimension value. Return null if
	 *         <code>relativeValue</code> has the unit which is not in the
	 *         above list.
	 */
	DimensionValue computeRelativeValue( DimensionValue fontSizeValue,
			DimensionValue relativeValue )
	{
		assert CSSLengthValueHandler.isAbsoluteUnit( fontSizeValue.getUnits( ) );
		if ( !CSSLengthValueHandler.isAbsoluteUnit( fontSizeValue.getUnits( ) ) )
		{
			throw new IllegalArgumentException(
					"The argument \"fontSizeValue\" should be absolute." ); 
		}
		if ( CSSLengthValueHandler.isAbsoluteUnit( relativeValue.getUnits( ) ) )
		{
			return relativeValue;
		}
		
		if ( DesignChoiceConstants.UNITS_EM.equals( relativeValue.getUnits( ) ) )
		{
			return new DimensionValue( fontSizeValue.getMeasure( )
					* relativeValue.getMeasure( ), fontSizeValue.getUnits( ) );
		}
		else if ( DesignChoiceConstants.UNITS_EX.equals( relativeValue