handle the gridviewdecimalcolumn exception

i have 2 questions please:

1 - I have a radgridview with a column that have a gridviewdecimalcolumn editor, i designed it to accept only 1 byte number , but at run time if the user enter a number  greater than 1 byte, an exception will occured: overflow exception was unhandled,  Value was either too large or too small for an unsigned byte.

and then application crashed and exit. how to handle this exception as a message for the user , so that the  user can enter a new number in the cell, without closing the application, .

2- other decimal  columns have a null value come from the databse, when i'm  trying to edit the cell  to enter a new value by clicking over it ,

a NullRefrenceException was unhandled will be thrown. and as

thanks.