Gnats 6053: Series Aggregation 'Error on NaN', no error when NaN is not relevant.
Bug Number: 6053
Release notes (y/n): Yes, maybe.
For Release Nums: 7.2

Gnats 6053: Series Aggregation 'Error on NaN' shouldn't consider unused 
  timesteps with 'First' or 'Last' agg functions.

The Series Time aggregation functions in RiverWare (e.g. in the Time 
Aggregation Series Slot) support these three ways of handling NaNs in the 
input time series:

  (1) Ignore NaNs
  (2) Do not aggregate intervals having NaNs
  (3) Error on NaN (excluding pre-simulation timesteps)

In the last case ("Error on NaN"), we are deciding that -- for the "First 
timestep" and "Last timestep" aggregation functions -- we don't want NaNs 
in OTHER timesteps to generate an error.

See the change in method: SeriesSlot::TimeAggSpec::recomputeOwnerSlot() 
in source file: Sim/SeriesSlot.TimeAgg.cpp.

SEE ALSO info about OTHER RECENT enhancements to time aggregation functions:
Set Timestep Size, Synchronize Slots, New NaN Option for RiverWare 7.2 / Dec 2017
R:\doc\runControl\InputAggregation\SetTstepSize-SyncSlotsNanOptions-RW72-Enh.docx
http://cadswes2.colorado.edu/~philw/2017/bugs/6036/SetTstepSize-SyncSlotsNanOptions-RW72-Enh.html

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