fix: source_column_name none (#661)

* fix: source_column_name none

source_column_name need a [none test](https://stackoverflow.com/questions/19614027/jinja2-template-variable-if-none-object-set-a-default-value) not "!="

* Update CHANGELOG.md

Author: kmclaugh

CHANGELOG.md

@@ -72,6 +72,7 @@ After:
 - Add Snowflake specific implementation of `deduplicate()` ([#543](https://github.com/dbt-labs/dbt-utils/issues/543), [#548](https://github.com/dbt-labs/dbt-utils/pull/548))
 
 ## Fixes
+- Fix `union_relations` `source_column_name` none option.
 - Enable a negative part_number for `split_part()` ([#557](https://github.com/dbt-labs/dbt-utils/issues/557), [#559](https://github.com/dbt-labs/dbt-utils/pull/559))
 
 ## Quality of life

macros/sql/union.sql

@@ -85,7 +85,7 @@
         (
             select
 
-                {%- if source_column_name != none %}
+                {%- if source_column_name is not none %}
                 cast({{ dbt_utils.string_literal(relation) }} as {{ type_string() }}) as {{ source_column_name }},
                 {%- endif %}