Can't export images in 2021

[cgmorton]

I think the problem is that the code is trying to select the CDL image that corresponds with the image year but there is not a 2021 CDL image yet. It seems like a simple fix for this would be to set clamp the year in the lc_mask function to 2008-2020.

So change this line:

year_condition = ee.Algorithms.If(ee.Number(year).lte(2007), 2008, year)

to something like this:

year_condition = ee.Number(year).max(2008).min(2020)

The problem with this fix is that this will need to be manually updated in the future. A better approach would be to get the last available CDL image year and clamp to that. I haven't tested this yet, but something like this might work for getting the max (and min) year:

year_max = ee.Date(ee.ImageCollection('USDA/NASS/CDL')
    .limit(1, 'system:time_start', false).first().get('system:time_start')).get('year')

[cgmorton]

I made the quick fix for this issue in order to start generating images for 2021, but I'm going to leave this open until I add some tests to make sure the dynamic year computation is working correctly.