NullPointerException when using only Mapping#target in mapping inheritance  #2139

This is as a result of the #2101 implementation

See: #2140

Internal error in the mapping processor: java.lang.NullPointerException at java.lang.String.startsWith(String.java:1405) at java.lang.String.startsWith(String.java:1434) at org.mapstruct.ap.internal.model.source.MappingMethodOptions.elementsAreContainedIn(MappingMethodOptions.java:241) at org.mapstruct.ap.internal.model.source.MappingMethodOptions.isRedefined(MappingMethodOptions.java:233) at org.mapstruct.ap.internal.model.source.MappingMethodOptions.addAllNonRedefined(MappingMethodOptions.java:223) at org.mapstruct.ap.internal.model.source.MappingMethodOptions.applyInheritedOptions(MappingMethodOptions.java:203) at org.mapstruct.ap.internal.processor.MapperCreationProcessor.mergeInheritedOptions(MapperCreationProcessor.java:463)