[Bug]: Map on empty list breaks durable execution

[eruvanos]

Expected Behavior

Map step should finish when a emptylist is given

Actual Behavior

Function stops executing and times out after a while.

Steps to Reproduce

Deploy durable function with following code

from aws_durable_execution_sdk_python import (
    durable_execution,
    DurableContext,
    durable_step,
)

@durable_execution
def lambda_handler(event, context: DurableContext):
    items = []

    _ = context.map(
            items,
            map_items,
            name="ProcessItems",
    )

def map_items(
    context: DurableContext,
    item,
    index,
    items,
) -> str:
    context.logger.info(
        f"Processing item {item}"
    )
    return "OK"

SDK Version

1.3.0

Python Version

3.14

Is this a regression?

No

Last Working Version

No response

Additional Context

No response

[yaythomas]

Calling the invoke API action failed with this message:

{
  "errorMessage": "max_workers must be greater than 0",
  "errorType": "CallableRuntimeError"
}

[yaythomas]

repro

def test_map_with_empty_list_should_not_hang():
    """Test that map with empty list completes immediately
    """
    items = []

    def map_func(ctx, item, idx, items):
        return f"processed_{item}"

    mock_state = Mock()
    mock_state.durable_execution_arn = "arn:test"

    parent_checkpoint = Mock()
    parent_checkpoint.is_succeeded.return_value = False
    parent_checkpoint.is_failed.return_value = False
    parent_checkpoint.is_existent.return_value = False

    mock_state.get_checkpoint_result = Mock(return_value=parent_checkpoint)
    mock_state.create_checkpoint = Mock()

    context = create_test_context(state=mock_state)

    # This should complete immediately, not hang
    result = context.map(
        items,
        map_func,
        name="EmptyMap",
    )

    # Should return empty BatchResult
    assert isinstance(result, BatchResult)
    assert len(result.all) == 0
    assert result.total_count == 0
    assert result.success_count == 0
    assert result.failure_count == 0

[yaythomas]

thanks for a great bug report @eruvanos, it was very helpful to have the immediate repo!

pr with fix out now