Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
{
					return element.getColumnName( );
				}
			}
		}
		return null;
	}
	private void updateButtons( )
	{
		boolean okEnable = true;
		Iterator iter = inputParameterGroup.getParameters( ).iterator( );
		if ( !iter.hasNext( ) )
		{
			okEnable = false;
		}
		else
		{
			int count = 0;
			while ( iter.hasNext( ) )
			{
				Object obj = iter.next( );
				if ( obj instanceof ScalarParameterHandle )
				{
					ScalarParameterHandle param = (ScalarParameterHandle) obj;
					count++;
					if ( !checkParameter( param ) )
					{
						okEnable = false;
						break;
					}