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/model/data/util/DataSwitch.java
if ( result == null )
					result = caseDataSet( numberDataSet );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.ORTHOGONAL_SAMPLE_DATA :
			{
				OrthogonalSampleData orthogonalSampleData = (OrthogonalSampleData) theEObject;
				Object result = caseOrthogonalSampleData( orthogonalSampleData );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.QUERY :
			{
				Query query = (Query) theEObject;
				Object result = caseQuery( query );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.RULE :
			{
				Rule rule = (Rule) theEObject;
				Object result = caseRule( rule );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}