This is with 3.5 beta 4

In getClientRecords(), the code,

EscherRecord r = Shape.getEscherChild(getSpContainer(), EscherClientDataRecord.RECORD_ID);
            //ddf can return EscherContainerRecord with recordId=EscherClientDataRecord.RECORD_ID
            //convert in to EscherClientDataRecord on the fly
            if(!(r instanceof EscherClientDataRecord)){

getEscherChild(...) may return null, in which,

!(r instanceof EscherClientDataRecord)

is true, and 

byte[] data = r.serialize();

throws a NullPointerException

java.lang.NullPointerException
	at org.apache.poi.hslf.model.SimpleShape.getClientRecords(SimpleShape.java:322)
	at org.apache.poi.hslf.model.SimpleShape.getClientDataRecord(SimpleShape.java:307)
	at org.apache.poi.hslf.model.TextShape.getPlaceholderAtom(TextShape.java:547)
	at org.apache.poi.hslf.model.Sheet.getPlaceholder(Sheet.java:408)
	at org.apache.poi.hslf.model.HeadersFooters.isVisible(HeadersFooters.java:244)
	at org.apache.poi.hslf.model.HeadersFooters.isHeaderVisible(HeadersFooters.java:148)
	at org.apache.poi.hslf.extractor.PowerPointExtractor.getText(PowerPointExtractor.java:173)
	at org.apache.poi.hslf.extractor.PowerPointExtractor.getText(PowerPointExtractor.java:144)