Created attachment 25525 [details]
PPTX showing NPE

When Tika tried to read metadata from a PPTX that has a null creation date, an NPE occurs in PackagePropertiesPart.getDateValue. 

	private String getDateValue(Nullable<Date> d) {
		if (d == null) {
			return "";
		}
		SimpleDateFormat df = new SimpleDateFormat(
				"yyyy-MM-dd'T'HH:mm:ss'Z'");
		return df.format(d.getValue());
	}

Although the code checks whether d is null, it appears that d.getValue() returns null, and an NPE is thrown in SimpleDateFormat.format:

Caused by: java.lang.NullPointerException
	at java.util.Calendar.setTime(Calendar.java:1075)
	at java.text.SimpleDateFormat.format(SimpleDateFormat.java:876)
	at java.text.SimpleDateFormat.format(SimpleDateFormat.java:869)
	at java.text.DateFormat.format(DateFormat.java:316)
	at org.apache.poi.openxml4j.opc.internal.PackagePropertiesPart.getDateValue(PackagePropertiesPart.java:587)