Printing the result of a run gives an error when flow_name is None

[ledell]

Description

TypeError thrown when calling the print method on a openml.runs.run.OpenMLRun object when flow_name is None.

Steps/Code to Reproduce

from sklearn import ensemble
from openml import tasks, flows, runs
import openml

task = tasks.get_task(3954)
clf = ensemble.RandomForestClassifier()
flow = flows.sklearn_to_flow(clf)
run = runs.run_flow_on_task(task, flow)
print(run) #error

Validating that the flow_name is None:

In [87]: run.flow_name is None
Out[87]: True

Expected Results

In [88]: print(run)
Out[88]: 
[run id: None, task id: 3954, flow id: 8656, flow name: None]

Actual Results

In [74]: print(run)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-74-7667ec7d87d4> in <module>()
----> 1 print(run)

/usr/local/lib/python3.6/site-packages/openml/runs/run.py in __str__(self)
 57 def __str__(self):
 58 flow_name = self.flow_name
---> 59 if len(flow_name) > 26:
 60 # long enough to show sklearn.pipeline.Pipeline
 61 flow_name = flow_name[:26] + "..."

TypeError: object of type 'NoneType' has no len()

Versions

Darwin-17.4.0-x86_64-i386-64bit
Python 3.6.5 (default, Apr 25 2018, 14:23:58)
[GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)]
NumPy 1.15.0
SciPy 1.1.0
Scikit-Learn 0.19.2
OpenML 0.7.0

[mfeurer]

Fixed by PR #563.