dbt docs generate fails when a column name is " "

Describe the bug

A clear and concise description of what the bug is. What command did you run? What happened?

Steps to reproduce

1. Create a model with a column name " " (I know)

$ cat models/customers.sql
select 1 as " "

1. Run dbt docs generate

(Note this also applies to source tables with this column name, but easiest to reproduce by creating a model)

Expected behavior

An error, but with a good message

Actual behaviour

Encountered an error:
None is not of type 'string'

Failed validating 'type' in schema['properties']['name']:
    {'type': 'string'}

On instance['name']:
    None

Screenshots and log output

2020-06-17 19:22:49.606297 (MainThread): Encountered an error:
2020-06-17 19:22:49.607069 (MainThread): None is not of type 'string'

Failed validating 'type' in schema['properties']['name']:
    {'type': 'string'}

On instance['name']:
    None
2020-06-17 19:22:49.611463 (MainThread): jsonschema.exceptions.ValidationError: None is not of type 'string'

Failed validating 'type' in schema['properties']['name']:
    {'type': 'string'}

On instance['name']:
    None

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/dbt/main.py", line 81, in main
    results, succeeded = handle_and_check(args)
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/dbt/main.py", line 159, in handle_and_check
    task, res = run_from_args(parsed)
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/dbt/main.py", line 212, in run_from_args
    results = task.run()
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/dbt/task/generate.py", line 249, in run
    catalog = Catalog(catalog_data)
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/dbt/task/generate.py", line 62, in __init__
    self.add_column(col)
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/dbt/task/generate.py", line 97, in add_column
    column = ColumnMetadata.from_dict(column_data)
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/hologram/__init__.py", line 594, in from_dict
    cls.validate(data)
  File "/Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/lib/python3.7/site-packages/hologram/__init__.py", line 937, in validate
    raise ValidationError.create_from(error) from error
hologram.ValidationError: None is not of type 'string'

Failed validating 'type' in schema['properties']['name']:
    {'type': 'string'}

On instance['name']:
    None

System information

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: ____________)

The output of dbt --version:

dbt --version
installed version: 0.18.0-b1
   latest version: 0.17.0

Your version of dbt is ahead of the latest release!

Plugins:
  - bigquery: 0.18.0b1
  - snowflake: 0.18.0b1
  - redshift: 0.18.0b1
  - postgres: 0.18.0b1

Additional context

• Might also happen if you have a column named 'null'.
• Here is the line of code

Workaround

Rename the column!

This often crops up if an existing relation (rather than a dbt-generated relation) has a strange column name. To find the column, use the information schema. For example, on Snowflake this would look like:

select * from <YOUR_DATABASE>.information_schema.columns
where (
    trim(column_name) = ''
    or column_name is null
    or lower(column_name) = 'null'
    or lower(column_name) = 'none'
) 

Make sure you check all databases that your dbt project references!

[clrcrl]

As the original bug report states, this can also happen when an existing table in your data warehouse has a poorly-named column! (The above instructions were to replicate the bug in the easiest way possible)

I’d suggest using the information schema to find any columns with a name that would get coerced to a null value.

If you’re using snowflake, this might look like:

select * from <YOUR_DATABASE>.information_schema.columns
where (
    trim(column_name) = ''
    or column_name is null
    or lower(column_name) = 'null'
    or lower(column_name) = 'none'
) 

Make sure you check it for all Snowflake databases that you use.

[clrcrl]

Resolved by #3499 (tested with the develop version of dbt)