Use null values instead of the empty dict for sql reporter

Change-Id: I23793e99e6ab6afdbe2f76a4433719a7f234ef5d

doc/source/admin/drivers/sql.rst

@@ -51,11 +51,12 @@ For example:
    - pipeline:
        name: post-merge
        success:
-         mydb_conn: {}
+         mydb_conn:
        failure:
-         mydb_conn: {}
+         mydb_conn:
 
 .. attr:: pipeline.<reporter>.<sql source>
 
-   To report to a database, add an empty dictionary to the desired
-   pipeline :ref:`reporter<reporters>` attributes.
+   To report to a database, add a key with the connection name and an
+   empty value to the desired pipeline :ref:`reporter<reporters>`
+   attributes.

tests/fixtures/config/sql-driver/git/common-config/zuul.yaml

@@ -7,12 +7,12 @@
     success:
       gerrit:
         Verified: 1
-      resultsdb: {}
+      resultsdb:
     failure:
       gerrit:
         Verified: -1
-      resultsdb: {}
-      resultsdb_failures: {}
+      resultsdb:
+      resultsdb_failures:
 
 - job:
     name: project-merge

zuul/driver/sql/sqlreporter.py

@@ -79,5 +79,5 @@ class SQLReporter(BaseReporter):
 
 
 def getSchema():
-    sql_reporter = v.Schema({})
+    sql_reporter = v.Schema(None)
     return sql_reporter