If I have analyzed the problem correctly the issue here is that Character#getNumericValue(ch) is returning -1 (perhaps -2) resulting in an error in your tile code. This is because it is reading all characters in the line, including whitespace characters.

The solution would be to do something like this inside of your for-loop where you create the tile:

// Inside of the for-loop...
if(i < line.length()) {
    char ch = line.charAt(i);
    int charValue = Character.getNumericValue(ch);

    // Checks if the character is an invalid character such as a whitespace.
    if (charValue == -1 || charValue == -2)
        continue;

    Tile t = new Tile(i, j, charValue);
    tiles.add(t);
}

If I have analyzed the problem correctly the issue here is that Character#getNumericValue(ch) is returning -1. This is because it is reading all characters in the line, including whitespace characters, which does not have a numeric value. The Character#getNumericValue(ch) javadocs read:

If the character does not have a numeric value, then -1 is returned.

The solution would be to do something like this inside of your for-loop where you create the tile:

// Inside of the for-loop...
if(i < line.length()) {
    char ch = line.charAt(i);
    int charValue = Character.getNumericValue(ch);

    // Checks if the character is an invalid character such as a whitespace.
    if (charValue == -1)
        continue;

    Tile t = new Tile(i, j, charValue);
    tiles.add(t);
}