Expected results

Layer type resets to default

Actual results

The entire page goes blank

Screenshots

![image](https://user-images.githubusercontent.com/8

Current behavior

When running the jupyter.jupyter.ExecuteNotebook task with output_format='html' the default settings for the HTMLExporter are used. There is no way to pass arguments to this exporter.

Proposed behavior

Allow passing arguments to the HTMLExporter.

Implementation suggestion

Something like html_exporter = nbconvert.HTMLExporter(**exporter_kwargs) on the

Describe the bug
Using a data source with umlauts in the column names leads to the Jupyter Notebook with which the suite can be edited throw an error on startup. The Notebook then doesn't load.
This might be a Jupyter Notebook bug, not sure?!

To Reproduce
Steps to reproduce the behavior:

1. Initialize a suite with this xlsx file as a data source (nothing fancy: Just two columns, the

Problem description

When I use the function of concatenating multiple columns, I find that it does not handle null values as expected.

This is the current output

df.concatenate_columns(["cat_1","cat_2","cat_3"],"cat",sep=",")

if they are not class methods then the method would be invoked for every test and a session would be created for each of those tests.

`class PySparkTest(unittest.TestCase):
@classmethod
def suppress_py4j_logging(cls):
logger = logging.getLogger('py4j')
logger.setLevel(logging.WARN)

@classmethod
def create_testing_pyspark_session(cls):
    return Sp