In Python, attempting to access an index or key of a NoneType object, which is an instance of the unique constant 'None' representing the absence of a value, leads to the 'NoneType' object is not subscriptable TypeError. This error commonly occurs when a variable is unintentionally assigned a NoneType due to uninitialized variables or functions returning None instead of an expected value. To resolve this issue, developers should ensure that variables are assigned appropriate values before accessing them and verify that objects are not None before attempting subscript operations. Additionally, employing best practices like checking for NoneType before accessing indices or keys can prevent the error. Tools like Rollbar can further aid in managing and analyzing such errors in real-time, facilitating smoother deployment of production code by automating error tracking and triaging.