optional search parameters in sql query and rows with null values

It's a fundamental property of NULL that when you compare it to anything—including NULL—it returns false, which is why what you're doing doesn't work.

So the first question to answer is: why do you want a row with a NULL lastname be returned when they enter a lastname of "smith"? Possibly you mean that either the firstname or the lastname needs to match to be returned, in which case you're not running the correct query. The most naive solution is:

SELECT firstname, lastname, ....
FROM profiles
WHERE IFNULL(firstName LIKE'%{firstname}%'
OR lastName LIKE '%{lastName}%'

Now this will work for several hundreds and possibly several thousand rows but won't scale beyond that for several reasons:

1. ORs are typically woeful in terms of performance. Avoid them where possible. If you look at database applications written by experienced programmers you probably won't find a single OR condition (except from those who proselytize the virtues of OR on the back of having once written a guestbook application that has 3 users and 2 hits a month);
2. Doing a LIKE with a % at the front will mean no indexes will be sued.

There are several solutions to (2). Probably the easiest in MySQL is to use full text searching on MyISAM tables. It won't find matches like "Johannes" if you type in "han" but it is generally sufficient.

Often you deal with OR conditions by using either UNION or (preferably) UNION ALL on multiple queries. For example:

SELECT firstname, lastname, ....
FROM profiles
WHERE firstName LIKE'%{firstname}%'
AND lastName LIKE '%{lastName}%'
UNION ALL
SELECT firstname, lastname, ....
FROM profiles
WHERE firstName LIKE'%{firstname}%'
AND lastname IS NULL
UNION ALL
SELECT firstname, lastname, ....
FROM profiles
WHERE firstName IS NULL
AND lastName LIKE '%{lastName}%'
UNION ALL
SELECT firstname, lastname, ....
FROM profiles
WHERE firstName IS NULL
AND lastName IS NULL

Looks big and ugly but UNION ALL scales extremely well (ignoring the % at the start of the LIKE criteria). It's basically concatenating (in this case) four queries. A UNION will do an implicit DISTINCT on the result rows but we know there'll be no overlap here because we're varying checking for NULL.

Another possibility is not to treat NULL as something you want to search for. This is a far better and more intuitive solution (imho). If someone types in a lastname of "Smith" do you really want rows with a NULL lastname showing up?

Or do you want them to show up because you might've got a match on the first name? If so, you want a slightly different query. For example:

SELECT firstname, lastname, ....
FROM profiles
WHERE id IN (
  SELECT id 
  FROM profiles
  WHERE firstName LIKE'%{firstname}%'
  UNION ALL
  SELECT id 
  FROM profiles
  WHERE lastName LIKE '%{lastName}%'
)

You can use COALESCE:

select firstname, lastname, ....
from profiles
where (coalesce(firstName, '') like '%{firstname}%')
AND (coalesce(lastName, '') like '%{lastName}%')

You could always disallow null values in the first place - after all, everybody must be alive for some positive number of years and be somewhere geographically.

If you absolutely must allow nulls, then either use COALESCE, as others have suggested, or possibly IFNULL which is MySQL specific and may be slightly more optimal since it takes exactly 2 paramters.