Null values in ODF files

[n-a-t-e]

It looks like OCE handes null values in ODF files well, but would be good to review how this works and how we will set appropriate attributes in ERDDAP. @JessyBarrette has started on this work

[pramod-thupaki]

Setting _FillValue attribute in the netcdf file at time of creation works well with ERDDAP in my experience. No changes need to be made on the 'datasets.xml' used by ERDDAP.

[JessyBarrette]

I believe OCE converts floats and time to NaN, haven't confirmed yet anything about Integers values.

Since addvar requests a null_value as an input. This had to be handle within the addvar integration of the different variables. Otherwise, just using a place holder like NaN would fail with integer variables.

[pramod-thupaki]

the null_value that you pass to add_var is designed to catch and convert values like '99' or '99.99' that are non-NaN null_values; you can also pass None or np.nan