How to ignore NaN values in gamma distribution?

Sir I want to fit my data with gamma distribution. If i want to find out the constants 'a' and 'b' by 'gamfit' with my data where some values are nan, then result is coming NaN. How to ignore the nan values in gamfit code so that i can get the correct result? plz help

phat=gamfit( A);

Where A has some NaN values