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/DataPackage.java
/**
	 * The feature id for the '<em><b>Base Sample Data</b></em>' containment reference list.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int SAMPLE_DATA__BASE_SAMPLE_DATA = 0;
	/**
	 * The feature id for the '<em><b>Orthogonal Sample Data</b></em>' containment reference list.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int SAMPLE_DATA__ORTHOGONAL_SAMPLE_DATA = 1;
	/**
	 * The feature id for the '<em><b>Ancillary Sample Data</b></em>' containment reference list.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int SAMPLE_DATA__ANCILLARY_SAMPLE_DATA = 2;
	/**
	 * The number of structural features of the '<em>Sample Data</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int SAMPLE_DATA_FEATURE_COUNT = 3;
	/**