Hey @Marvin, in prefect 3, we attempted to run a prefect flow that triggers subflows on an EC2 instance with a

DaskTaskRunner

but got the following error:

pydantic_core._pydantic_core.PydanticSerializationError: Error calling function `ser_model`: AttributeError: 'NullFileSystem' object has no attribute 'get_block_type_slug'

What could that cryptic error message mean?

The error message you're encountering,

pydantic_core._pydantic_core.PydanticSerializationError: Error calling function ser_model: AttributeError: 'NullFileSystem' object has no attribute 'get_block_type_slug'

, seems related to an issue with the file system being used in your Prefect configuration. Based on the Prefect 3.x documentation, this could be associated with how blocks are handled in Prefect. Blocks in Prefect are modular components that allow you to define configurations for infrastructure, storage, and more. The error might suggest that there's a misconfiguration or a missing setup regarding your file system or storage blocks. The

NullFileSystem

indicates that there might not be a properly initialized file system block or that Prefect cannot access the needed file system type to execute your flow. In the context of using the

DaskTaskRunner

, ensure that the Dask cluster and any file-related operations are correctly configured and accessible. You might want to examine the configuration of your Dask setup and any file storage options you are using. Here are some links that might be helpful: - Description of different block types in Prefect: Prefect Blocks - Information about Dask integration with Prefect: Prefect Dask Integration You might want to consider revisiting how you're specifying the file system or related blocks in your flow definition. Perhaps a minor configuration tweak will save the day!