arcpy.UpdateCursor setting value to 0 instead of Null

Question

I'm having issues setting a row value to 0 when joining a csv to a shapefile. When the shapefile value is not in the csv, the row is getting set to 0 instead of null. This is a huge problem as i'm showing 0 change instead of no data. I tried row.setValue(field, None) and row.setNull(field) and both produce the same result. In the .dbf file of the shapefile, there is no value but in the UI attribute table a 0 is shown.

arcpy.AddField_management(shpfile, "TEST", "DOUBLE", field_is_nullable = 'NULLABLE')

newcols = ["TEST"]

with open(csvfile, 'rb') as csvfile:
    lib = dict()
    csvfile = csv.reader(csvfile, delimiter = ",")
    csvfile.next() #skip the headers
    for line in csvfile:
        lib[line[csvjoinindex]] = lib.get(line[csvjoinindex],line[csvstartfield:])
rows = arcpy.UpdateCursor(shpfile)
for row in rows:
    shpjoinval = str(row.getValue(shapefilejoincol))
    try:
        vals = lib.get(shpjoinval)
        for ind, field in enumerate(newcols):
            row.setValue(str(field),vals[ind])
            rows.updateRow(row)
    except:
        for ind, field in enumerate(newcols):
             row.setNull(field)
             rows.updateRow(row)

Answer 1

You cannot output a Null value in a shapefile to a numeric field. This is part of the shapefile specification, so the specification will override every attempt you make to set a Null value. You have to output your data to a gdb (file gdb is best) feature class to use Null values in numeric fields.

The help under Geoprocessing considerations for shapefile output states:

"Null values are not supported in shapefiles. If a feature class containing 
 nulls is converted to a shapefile, then the null values will be
 changed into the following:

...
Number - When tool requires a NULL, infinity, or NaN (Not a Number) to be output.   -1.7976931348623158e+308 (IEEE standard for the maximum negative value)
Number (all other geoprocessing tools)  0
Text    " " (blank — no space)
Date    Stored as zero, but displays "<null>".""