Interpret an earlier Filecoin tipset returned for a requested epoch
A historical job requesting one row per epoch may receive a tipset whose recorded height is lower than the requested epoch. Filecoin can have epochs with no blocks.
Read the returned height explicitly
The example searches backward from the current heaviest chain for epoch 3000000. Record the requested epoch and returned Height separately, along with the full Cids array.
{"jsonrpc":"2.0","id":1,"method":"Filecoin.ChainGetTipSetByHeight","params":[3000000,[]]}
Represent the skipped epoch correctly
If the returned height is 2999999, do not label those blocks as mined at 3000000. Model the requested epoch as a null round on the sampled branch and reference the earlier tipset as its predecessor. For reproducible exports replace the moving head selector with the same anchor tipset throughout.