scrapy/scrapy — pull request #708 by nramirezuy (2014-04-29 15:37:27+00:00)
Title: Prevent hanging on invalid start_requests

There are cases where if the start_requests isn't an iterable scrapy hangs.

Some examples:
```python
def start_requests(self):
return None
```
```python
def start_requests(self):
pass
```
```python
def start_requests(self):
return Request()
```