STR:
create a custom blueprint
create a function that takes an array (ie, strings) as a parameter (TestFn)
extends the custom blueprint in JS with an override for TestFn
Call the function via a blueprint with some valid non-zero length array (ie, MakeArray node)
note that the array is empty when the JS executes.

Possible Fix (minimally tested locally)
in JavascriptContext_Private.cpp
UJavascriptGeneratedFunction::Thunk
when iterating properties to copy into NewStack.Locals, params that are CPF_OutParm should also check for CPF_ReferenceParm and if so, also copy it into Locals instead of only the out list.

bool bIsOutParm = Property->PropertyFlags & CPF_OutParm;;
bool bIsInParm = !bIsOutParam || ((Property->PropertyFlags & CPF_ReferenceParm) != 0);

uint8* Param = nullptr;
if (bIsInParam)
{
  Param = Property->ContainerPtrToValuePtr<uint8>(NewStack.Locals);
  Property->InitializeValue_InContainer(NewStack.Locals);
}
Stack.Step(Stack.Object, Param);

if (bIsOutParam)
... // everything from before except the call to Stack.Step, and no else clause