Bug 214212 Problem occurs when set the masterpage margin with ems/exs/pixcel units.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/metadata/DimensionPropertyType.java
/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.design.metadata.PropertyType#getTypeCode()
	 */
	public int getTypeCode( )
	{
		return DIMENSION_TYPE;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.design.metadata.PropertyType#getXmlName()
	 */
	public String getName( )
	{
		return DIMENSION_TYPE_NAME;
	}
	/**
	 * Converts the dimension property value to a locale-independent string. The
	 * string will be converted into a format like "#.###", there is no group
	 * separator and remains at most 3 digits after the decimal separator. e.g:
	 * "12,000,000.12345cm" will be converted into "12000000.123cm"
	 */
	public String toString( Module module, PropertyDefn defn, Object value )
	{
		if ( value == null )
			return null;
		return value.toString( );
	}