2715795 - "Mapping failed" exception with XSLT or JAVA Mapping after upgrade to 7.50

After upgrading the SAP Process Integration / Orchestration system to version 7.50, the previously working XSLT or JAVA Mappings are failing with the following exceptions:

Catching com.sap.aii.af.service.mapping.MappingException: Mapping failed
at com.sap.aii.ibrun.sbeans.mapping.MappingAccessBean.executeMapping(MappingAccessBean.java:201)
at sun.reflect.GeneratedMethodAccessor588.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)

or

Caused by: java.nio.charset.IllegalCharsetNameException:
at java.nio.charset.Charset.checkName(Charset.java:303)
at java.nio.charset.Charset.lookup2(Charset.java:484)
at java.nio.charset.Charset.lookup(Charset.java:464)
at java.nio.charset.Charset.forName(Charset.java:528)
at com.sap.engine.lib.xml.parser.helpers.ByteCharConverter.getByteToCharDecoder(ByteCharConverter.java:17)
at com.sap.engine.lib.xml.parser.helpers.SUNEncodings.<init>(SUNEncodings.java:44)
at com.sap.engine.lib.xml.parser.helpers.SUNEncodings.<init>(SUNEncodings.java:50)

or

Caused by: java.lang.NullPointerException: while trying to invoke the method com.sap.engine.interfaces.messaging.api.Payload.getContentType() of a null object returned from com.sap.engine.interfaces.messaging.api.Message.getMainPayload()

•  SAP NetWeaver 7.5

Process Orchestration 7.5, PI 7.5, PO 7.5, XI, AEX, IllegalCharsetNameException, Mapping failed, XSLT, JAVA Mapping, UDF, user defined function, user defined functions, Function, , KBA , BC-XI-IBC-MAP , Mapping , Problem