check that the data exists before sending it to wpdb

Hi the error you are getting for $serializedpaisol variable because it is not define in function scope.

the variable you define in specific scope can not access out form its scope;

eg.

{
//example scope
$var=10;
}
echo $var; // you will get undefined error.

how you can fixed it?

Solution

// first define variable in function  scope

$serializedpaisol ="";

if(isset($paisol)){ 
    $serializedpaisol = maybe_serialize($paisol);
}
echo $serializedpaisol; // now you will not get any error.

hope you understand the point.

Thanks