I was going through the server Event log the other day and noticed the following error.
The Execute method of job definition Microsoft.SharePoint.Administration.SPPasswordManagementJobDefinition (ID 2c784c63-26c9-4e2c-8dbf-f347222ed56b) threw an exception. More information is included below.
Object reference not set to an instance of an object.
Then I went to SharePoint Central Administration, Security, Configure Managed accounts and the page displayed “Object reference not set to an instance of an object” error message.
Some users suggested to remove and recreate the manage account using PowerShell command Remove-SPManagedAccount. That doable, but I found a better solution that does not require to recreate the managed account here. First, I ran the PowerShell command Get-SPManagedAccount to find out the account that caused the problem. Then I used the PowerShell command from here to remedy the problem.
Learn more about service and managed service Accounts from here.