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 = defaultCase( theEObject );
				return result;
			}
			case DataPackage.TEXT_DATA_SET :
			{
				TextDataSet textDataSet = (TextDataSet) theEObject;
				Object result = caseTextDataSet( textDataSet );
				if ( result == null )
					result = caseDataSet( textDataSet );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.TRIGGER :
			{
				Trigger trigger = (Trigger) theEObject;
				Object result = caseTrigger( trigger );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			default :
				return defaultCase( theEObject );
		}
	}
	/**
	 * Returns the result of interpretting the object as an instance of '<em>Action</em>'.
	 * <!-- begin-user-doc -->
	 * This implementation returns null; returning a non-null result will terminate the switch. <!-- end-user-doc -->