Update SQL to allow handling null columns

dbt/include/global_project/macros/materializations/models/incremental/merge.sql

@@ -62,12 +62,12 @@
 
     {% if unique_key %}
         {% if unique_key is sequence and unique_key is not string %}
-            delete from {{target }}
+            delete from {{ target }}
             using {{ source }}
             where (
                 {% for key in unique_key %}
-                    {{ source }}.{{ key }} = {{ target }}.{{ key }}
-                    {{ "and " if not loop.last}}
+                    ({{ source }}.{{ key }} = {{ target }}.{{ key }} or ({{ source }}.{{ key }} is null and {{ target }}.{{ key }} is null))
+                    {{ "and " if not loop.last }}
                 {% endfor %}
                 {% if incremental_predicates %}
                     {% for predicate in incremental_predicates %}

dbt/tests/adapter/incremental/test_incremental_unique_id.py

@@ -240,6 +240,8 @@
 select 'NY','New York','Manhattan','2021-04-01'
 union all
 select 'PA','Philadelphia','Philadelphia','2021-05-21'
+union all
+select 'CO','Denver',null,'2021-06-18'
 
 """
 
@@ -265,6 +267,8 @@
 select 'NY','New York','Manhattan','2021-04-01'
 union all
 select 'PA','Philadelphia','Philadelphia','2021-05-21'
+union all
+select 'CO','Devner',null,'2021-06-18'
 
 """
 
@@ -288,6 +292,7 @@
 NY,Kings,Brooklyn,2021-04-02
 NY,New York,Manhattan,2021-04-01
 PA,Philadelphia,Philadelphia,2021-05-21
+CO,Denver,,2021-06-18
 """
 
 seeds__add_new_rows_sql = """