The correct answer is D. | eval notNULL = "" fillnull value=0 notNULL
* Option A is incorrect because it is missing a comma between the "0" and the notNULL in the if function. The correct syntax for the if function is if (condition, true_value, false_value).
* Option B is incorrect because it is missing the false_value argument in the if function. The correct syntax for the if function is if (condition, true_value, false_value).
* Option C is incorrect because it uses the nullfill command, which only replaces null values, not empty strings. The nullfill command is equivalent to fillnull value=null.
* Option D is correct because it uses the eval command to assign an empty string to the notNULL field, and then uses the fillnull command to replace the empty string with a zero. The fillnull command can replace any value with a specified replacement, not just null values.