Final answer:
An AssertionError related to Gulp indicates a missing task function in the configuration, and it can be resolved by ensuring that each task set in Gulp is linked to a specific function.
Step-by-step explanation:
An AssertionError [ERR_ASSERTION] in the context of using Gulp indicates that there was an expectation within the code that was not met. Specifically, when configuring tasks in Gulp, a task function must be provided. Gulp uses these task functions to define various operations such as compiling code, running tests, or minifying files. The Gulp set method is a way to assign such tasks to be executed during the build process. If Gulp encounters a situation where a task is set without an associated function, it throws an AssertionError as a signal that the task configuration is incorrect. To resolve this error, ensure that each task you define with Gulp set has a corresponding function that contains the code meant to be executed when the task runs.