public static FieldUpdate createClear(Field field) {
        return new FieldUpdate(field, ValueUpdate.createClear());
    }
Creates a new field update, with one encapsulated value update,
that clears the value; see documentation for ClearValueUpdate to see behavior
for the individual data types. Note that clearing the value is not the same
clearing the field; this method leaves an empty value, whereas clearing the
field will completely remove the value.

@param field the field to clear the value of
@return a FieldUpdate specifying the clearing
@see com.yahoo.document.update.ClearValueUpdate
@see ValueUpdate#createClear()
@see FieldUpdate#createClearField(com.yahoo.document.Field)
document/src/main/java/com/yahoo/document/update/FieldUpdate.java