File upload works only if all fields are filled in - php

Question

I have a form where users have the option to upload up to 4 files. They do not have to upload all 4.
If they upload 4 files my script works fine. If they upload less than this I get an error "Notice: Undefined index: extension" on the lines in the filenamefetch section that start
$fileName2 = uniqid() . '.' . $fileData2["extension"]; for each of the empty files.
How can I hide this error message? The rest of the script operates as I would expect.
<?php
require_once("connect_db.php");
$ajax_result = "error";
$employeeid=$_POST['employeeid'];
$file1type=$_POST['file1type'];
$file1date=$_POST['file1date'];
$file2type=$_POST['file2type'];
$file2date=$_POST['file2date'];
$file3type=$_POST['file3type'];
$file3date=$_POST['file3date'];
$file4type=$_POST['file4type'];
$file4date=$_POST['file4date'];
//file data fetch
$fileData1 = pathinfo(basename($_FILES["file1"]["name"]));
$fileName1 = uniqid() . '.' . $fileData1["extension"];
$target_path1 = ("uploads/" . $fileName1);
$fileData2 = pathinfo(basename($_FILES["file2"]["name"]));
$fileName2 = uniqid() . '.' . $fileData2["extension"];
$target_path2 = ("uploads/" . $fileName2);
$fileData3 = pathinfo(basename($_FILES["file3"]["name"]));
$fileName3 = uniqid() . '.' . $fileData3['extension'];
$target_path3 = ("uploads/" . $fileName3);
$fileData4 = pathinfo(basename($_FILES["file4"]["name"]));
$fileName4 = uniqid() . '.' . $fileData4['extension'];
$target_path4 = ("uploads/" . $fileName4);
//image 1
while(file_exists($target_path1))
{
$fileName1 = uniqid() . '.' . $fileData1['extension'];
$target_path1 = ("uploads/" . $fileName1);
}
if (move_uploaded_file($_FILES['file1']['tmp_name'], $target_path1))
{ // The file is in the images/gallery folder. Insert record into database by
$q5="INSERT INTO uploadedfiles (filetype, employeeid, filename, filedate) VALUES('$file1type', '$employeeid','$fileName1', '$file1date')";
$r5 = mysqli_query($dbc, $q5) or die(mysqli_error($dbc));
echo "file 1 uploaded";} else {echo "";}
//image 2
while(file_exists($target_path2))
{
$fileName2 = uniqid() . '.' . $fileData2['extension'];
$target_path2 = ("uploads/" . $fileName2);
}
if (move_uploaded_file($_FILES['file2']['tmp_name'], $target_path3))
{ // The file is in the images/gallery folder. Insert record into database by
$q6="INSERT INTO uploadedfiles (filetype, employeeid, filename, filedate) VALUES('$file2type', '$employeeid','$fileName2', '$file2date')";
$r6 = mysqli_query($dbc, $q6);
echo "";} else {echo "";}
//image 3
while(file_exists($target_path3))
{
$fileName3 = uniqid() . '.' . $fileData3['extension'];
$target_path3 = ("uploads/" . $fileName3);
}
if (move_uploaded_file($_FILES['file3']['tmp_name'], $target_path3))
{ // The file is in the images/gallery folder. Insert record into database by
$q7="INSERT INTO uploadedfiles (filetype, employeeid, filename, filedate) VALUES('$file3type', '$employeeid','$fileName3', '$file3date')";
$r7 = mysqli_query($dbc, $q7);
echo "";} else {echo "";}
//image 4
while(file_exists($target_path4))
{
$fileName4 = uniqid() . '.' . $fileData4['extension'];
$target_path4 = ("uploads/" . $fileName4);
}
if (move_uploaded_file($_FILES['file4']['tmp_name'], $target_path4))
{ // The file is in the images/gallery folder. Insert record into database by
$q8="INSERT INTO uploadedfiles (filetype, employeeid, filename, filedate) VALUES('$file4type', '$employeeid','$fileName4', '$file4date')";
$r8 = mysqli_query($dbc, $q8);
echo "";} else {echo "";}