How to verify is an array of cells is null in java?

The "null" character is '\0', so you can compare if grid[i][j] == '\0'.

The literal null is for reference types, which char is not.

Primitive arrays such as your char[][] can't contain null. Only object arrays can hold nulls. You could convert your array to Character[][] instead.

Thanks to autoboxing your existing code should work just fine, but now you can actually put nulls in it.

In my case that would mean null because I initialize an empty char array

Incorrect. The default value of a char is '\0', e.g. new char[3][4] creates an outer arrays of 3 sub-arrays, and each sub-array contains 4 '\0' values.

So, your if statement should be:

if (grid[i][j] == '\0')