Call summary on "counternull" class to retrieve range of counternull values.
Call plot on "counternull" class for visualization
of counternull distribution.
Argument "counts" must contain whole numbers for bounds.Lower bound must be
smaller than upper bound. If argument is not specified, counternull values
will be obtained using the "counts" argument from the specified "null_rand"
argument.
If no counternull values are found, all entries in class are set to null.
If only one set of counternull values are found, "perm_two", low_two"
and "high_two" are set to null.