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
if ( defaultFontSizeValue == null )
		{
			ElementDefn styleDefn = (ElementDefn) MetaDataDictionary
					.getInstance( ).getElement(
							ReportDesignConstants.STYLE_ELEMENT );
			ElementPropertyDefn fontSizePropDefn = (ElementPropertyDefn) styleDefn
					.getProperty( IStyleModel.FONT_SIZE_PROP );
			Object defaultValue = fontSizePropDefn.getDefault( );
			if ( defaultValue instanceof DimensionValue )
				defaultFontSizeValue = (DimensionValue) defaultValue;
			defaultFontSizeValue = provider.getValueOf( (String) defaultValue );
		}
		return defaultFontSizeValue;
	}
	
	/**
	 * Computes the dimension value which is relative to font size. The units
	 * which can be computed are:
	 * <ul>
	 * <li>UNITS_EM
	 * <li>UNITS_EX
	 * <li>UNITS_PERCENTAGE
	 * </ul>
	 * <p>
	 * The following shows the computation rule. For example, font size = 12px
	 * <p>
	 * 2em = 12px * 2(em) = 24px
	 * <p>
	 * 4ex = 12px * 4(ex) / 2 = 24px
	 * <p>