[BUG] column_list null in unique_combination_of_columns

[paulleblond]

Describe the bug
DBT Fusion reports an error attempting to compile with the unique_combination_of_columns test and the quote_columns argument set to true. This code compiles correctly in the latest version of DBT Cloud.

error: dbt1501: Failed to render SQL unknown method: none has no method named append
(in target\generic_tests\unique_combination_of_columns__0d5ec3e41a387f7d06bfb53631f828b7.sql:1:1)
(in dbt_packages\dbt_utils\macros\generic_tests\unique_combination_of_columns.sql:2:29)
(in dbt_packages\dbt_utils\macros\generic_tests\unique_combination_of_columns.sql:12:45)
--> target\generic_tests\unique_combination_of_columns__0d5ec3e41a387f7d06bfb53631f828b7.sql:1:1

What version of dbt Fusion is this bug in? (find out by running dbt --version)
2.0.0-preview.63

Is this a discrepancy between the dbt Fusion Engine and dbt Core? Check one.

• YES
• NO

To Reproduce
Build a model with the following YML. The quote_columns is required to cause the error.

  - name: MODEL_NAME
    constraints:
      - type: primary_key
        columns: [columna, columnb]
    tests:
      - dbt_utils.unique_combination_of_columns:
          arguments:
            combination_of_columns:
              - columna
              - columnb
            quote_columns: true

Expected behavior
Expect the code to compile without error.

Screenshots
N/A

Operating System and CPU Type (please complete the following information):

• Windows
• X86