Removing chars(unicode) that is not supported by font

Hi Everyone.

I need a help on removing unsupported characters by the font before write
it into pdf.

For example:

I am using Lato Font. And I see that unicode u'\u2036' (REVERSED DOUBLE
PRIME) is not supported by Lato Font. So its displaying "notdef"
character(a question mark with box around it). But I want to remove
characters like this that doesn't supported by the font.

Basically I want to custom "notdef" to null character so that it removes it
in pdf. Any way to do this? How do I solve this problem?


Thanks in advance