According to an errata to the spec:

2.48. Section 14.1. Spec states that an empty sequence that is the content of a complex type
is a schema definition error. Many schema processors are not able to distinguish this
condition from a complex type with no content at all (it is not required to do so by the XML
Schema specification). As a complex type with no content is not useful in DFDL, change the
spec to state that both conditions are schema definition errors.

Note that this case is for complexTypes with NO content, not to be confused (and I confused them at length) with complexTypes with EMPTY content.

Instead of a neatly packaged SDE I get this error:

[info] - test_noContentComplexSDE *** FAILED ***
[info] edu.illinois.ncsa.daffodil.exceptions.Abort: scala.MatchError: List() (of class scala.collection.immutable.Nil$)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGValue.edu$illinois$ncsa$daffodil$dsom$oolag$OOLAG$OOLAGValue$$oolagTryCatch(OOLAG.scala:501)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGValue$$anonfun$6.apply(OOLAG.scala:577)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGHost.circularityDetector(OOLAG.scala:234)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGValue.valueAsAny(OOLAG.scala:563)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$LV.value(OOLAG.scala:659)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGHost$$anonfun$checkErrors$1$$anonfun$apply$mcV$sp$2$$anonfun$apply$2.apply$mcV$sp(OOLAG.scala:332)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGHost$$anonfun$checkErrors$1$$anonfun$apply$mcV$sp$2$$anonfun$apply$2.apply(OOLAG.scala:314)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGHost$$anonfun$checkErrors$1$$anonfun$apply$mcV$sp$2$$anonfun$apply$2.apply(OOLAG.scala:314)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$.keepGoing(OOLAG.scala:75)
[info] at edu.illinois.ncsa.daffodil.dsom.oolag.OOLAG$OOLAGHost$$anonfun$checkErrors$1$$anonfun$apply$mcV$sp$2.apply(OOLAG.scala:314)
[info] ...

The test is noContentComplexSDE in the following files:
daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section14/sequence_groups/SequenceGroup.tdml
daffodil-test/src/test/scala-debug/edu/illinois/ncsa/daffodil/section14/sequence_groups/TestSequenceGroupsDebug.scala
daffodil-test/src/test/scala/edu/illinois/ncsa/daffodil/section14/sequence_groups/TestSequenceGroups.scala