Given a `NxN` matrix. Fill the integers from `1` to `n*n` to this matrix that makes the sum of each row, each column and the two diagonals equal.\n\n**Example 1:**\n```\nInput: n = 2\nOutput: null\nExplanation: We need to fill [1, 2, 3, 4] into a 2x2 matrix, which is not possible so return null.\n```\n\n**Example 2:**\n```\nInput: n = 3\nOutput:\n[[8, 3, 4],\n [1, 5, 9],\n [6, 7, 2]]\nExplanation: We need to fill [1, 2, 3... 9] into a 3x3 matrix. This is one way to do it\nEach row [8, 3, 4] [1, 5, 9] [6, 7, 2] sum is 15.\nEach column [8, 1, 6] [3, 5, 7] [4, 9, 2] sum is 15.\nThe two diagonals [8, 5, 2] [4, 5, 6] sum is 15.\n```\n\n```\nint[][] fillMatrix(int n) {\n}\n```

Given a NxN matrix. Fill the integers from 1 to n*n to this matrix that makes the sum of each row, each column and the two diagonals equal.\n\nExample 1:\n\nInp