Grid Path with Obstacle Removal

You are given a 2D grid of integers where each cell is either 0 or 1. Here, 0 represents an empty cell and 1 represents an obstacle. You need to find the shortest path from the top-left corner (grid[0][0]) to the bottom-right corner (grid[m-1][n-1]). You can move up, down, left, or right at each step. Additionally, you are allowed to remove at most one obstacle (i.e., change a single 1 to a 0) during your journey.

Write a function that accepts the grid as input and returns the length of the shortest path if it exists. If there is no valid path, return -1. The length of the path is defined as the number of cells traversed, including the starting and ending cells.

Constraints:

• The grid will have dimensions m x n where m and n are positive integers.
• The grid cells contain only 0s and 1s.
• You can remove at most one obstacle.

Example:

For the following grid:

[[0, 1, 0, 0, 0],
 [0, 1, 0, 1, 0],
 [0, 0, 0, 1, 0],
 [1, 1, 1, 0, 0]]

A possible valid shortest path after removing one obstacle might have a length of 8. (Note: The exact path may vary depending on which obstacle is removed.)

Implement your solution in the programming language of your choice. Ensure that your code is modular and includes appropriate error handling for invalid inputs.