Bug 207250 Check blank value for datetime type parameter from url.[0002][0705]
Description: Check blank value for datetime type parameter from url. Build number:2.3.0.v20071023 Steps to reproduce: 1. New a datetime parameter mydt,listbox, tick off isRequired. 2. Preview in external browser and add "&dt=" in url, press enter. Expected result: Error message to indicate blank value isn't allowed for this parameter. Actual result: No error message and blank value is accepted. I tried to new a jsp and use <birt:paramDef> to pass the blank value and the blank value is accepted,too. Error log:n/a
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/utility/DataUtil.java
obj = ParameterValidationUtil.validate( dataType,
					getDefaultDateFormat( dataType ), value );
		}
		return obj;
	}
	/**
	 * Gets the display string for the value with default locale and default
	 * format, The value must be the valid data type. That is:
	 * 
	 * <ul>
	 * <li>if data type is <code>PARAM_TYPE_DATETIME</code>, then the value
	 * must be <code>java.util.Date<code>.</li>
	 * <li>if the data type is <code>PARAM_TYPE_FLOAT</code>, then the value must
	 * be <code>java.lang.Double</code>.</li>
	 * <li>if the data type is <code>PARAM_TYPE_DECIMAL</code>, then the value must
	 * be <code>java.math.BigDecimal</code>.</li>
	 * <li>if the data type is <code>PARAM_TYPE_BOOLEAN</code>, then the value must
	 * be <code>java.lang.Boolean</code>.</li>
	 * <li>if the data type is <code>PARAM_TYPE_STRING</code>, then the value must
	 * be <code>java.lang.String</code>.</li>
	 * </ul>
	 * 
	 * @param value
	 *  		the input value to validate
	 * @return the formatted string
	 */
	public static String getDisplayValue( Object value )
	{
		if ( value == null )