How to deal with empty array keys in a foreach that is inside a while loop?

I have the following array which is being generated from a msqli query.

Array
(
    [0] => 21
    [1] => AAAAA
    [2] => BBBBB
    [3] => 1234567
    [4] => aaa
    [5] => bbb
    [6] => ccc
    [7] => ddd
    [8] => 2015-01-19 03:31:33
    [9] => 1
    [10] => 5
    [11] => 5, - not set -;9, - not set -;10, - not set -;11, - not set -;14, - not set -;19, 12;20, mm_cb_on;21, - not set -;27, Noe;28, Pena;62, mm_cb_off
)

Array
(
    [0] => 22
    [1] => AAAAA
    [2] => BBBBB
    [3] => 1234567
    [4] => aaa
    [5] => bbb
    [6] => ccc
    [7] => ddd
    [8] => 2015-01-19 03:31:33
    [9] => 1
    [10] => 6
    [11] => 5, - not set -;9, - not set -;10, - not set -;11, - not set -;14, - not set -;20, mm_cb_on;21, - not set -;
)

Array
(
    [0] => 23
    [1] => AAAAA
    [2] => BBBBB
    [3] => 1234567
    [4] => aaa
    [5] => bbb
    [6] => ccc
    [7] => ddd
    [8] => 2015-01-19 03:31:33
    [9] => 1
    [10] => 7
    [11] => 5, - not set -;11, - not set -;14, - not set -;19, 23;20, mm_cb_on;21, - not set -;27, Noe;28, Pena;62, mm_cb_off
)

I am looping through this data like so:

while ($row = mysqli_fetch_array($data)) {
    echo "<td nowrap>" .$row{'first_name'}. "</td>
          <td nowrap>" .$row{'last_name'}. "</td>
          .......";
}

When I get to the last key in the array, I am looping through that data, and exploding like this:

while ($row = mysqli_fetch_array($data)) {
    echo "<td nowrap>" .$row{'first_name'}. "</td>
          <td nowrap>" .$row{'last_name'}. "</td>
          .......";
    $custom_fields = $row[11];
    $fields = explode(";", $custom_fields);
    foreach ($fields as $keys) {
        $key = explode(',', $keys);

        var_dump($key);
    }
}

That var dump produces the following array structure (for the first key in the previous array):

Array
(
    [0] => 5
    [1] =>  - not set -
)
Array
(
    [0] => 9
    [1] =>  - not set -
)
Array
(
    [0] => 10
    [1] =>  - not set -
)
Array
(
    [0] => 11
    [1] =>  - not set -
)
Array
(
    [0] => 14
    [1] =>  - not set -
)
Array
(
    [0] => 19
    [1] =>  12
)
Array
(
    [0] => 20
    [1] =>  mm_cb_on
)
Array
(
    [0] => 21
    [1] =>  - not set -
)
Array
(
    [0] => 27
    [1] =>  Noe
)
Array
(
    [0] => 28
    [1] =>  Pena
)
Array
(
    [0] => 62
    [1] =>  mm_cb_off
)

I am trying to create conditionals like so:

if (isset($key[0]) && $key[0] == 19) { // this produce none for every row
    $prov_id = $key[1];
} else {
    $prov_id = 'None';
}

if ($key[0] == 27) {
    $fm2_fname = $key[1];
} else {
    $fm2_fname  = '';
}

if ($key[0] == 28) {
    $fm2_lname = $key[1];
} else {
    $fm2_lname  = '';
}

The problem I am having is in the loop some of the items do not have $key[0] == "19" ... How would I handle this inside the foreach loop? Any help is greatly appreciated.