esgf_query() did not accept empty resolution

[hongyuanjia]

library(epwshiftr)

esgf_query(variable = "tas", resolution = NULL)
#> No matched data. Please check network connection and the availability of LLNL ESGF node.
#> Null data.table (0 rows and 0 cols)

^{Created on 2021-02-01 by the reprex package (v0.3.0)}