Bug 202254 Exception is thrown when category values are null and type of X axis is set to DateTime
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/util/CDateTime.java
return cdt.getActualMaximum( Calendar.DAY_OF_YEAR );
	}
	/**
	 * A convenience method provided to return the number of milliseconds
	 * available in a given unit
	 * 
	 * @param iUnit
	 *            The unit for which the number of milliseconds are to be
	 *            computed
	 * 
	 * @return The number of milliseconds for the specified unit
	 */
	public static final double inMillis( int iUnit )
	{
		if ( iUnit == Calendar.SECOND )
		{
			return MILLIS_IN_SECOND;
		}
		else if ( iUnit == Calendar.MINUTE )
		{
			return MILLIS_IN_MINUTE;
		}
		else if ( iUnit == Calendar.HOUR )
		{
			return MILLIS_IN_HOUR;
		}
		else if ( iUnit == Calendar.DATE )
		{
			return MILLIS_IN_DAY;
		}