Fixed PostgreSQL tests

Author: morozov

lib/Doctrine/DBAL/Platforms/PostgreSqlPlatform.php

@@ -399,9 +399,9 @@ public function getListTableColumnsSQL(string $table, ?string $database = null)
                      WHERE c.oid = pg_attrdef.adrelid
                         AND pg_attrdef.adnum=a.attnum
                     ) AS default,
-                    (SELECT pg_description.description
+                    COALESCE((SELECT pg_description.description
                         FROM pg_description WHERE pg_description.objoid = c.oid AND a.attnum = pg_description.objsubid
-                    ) AS comment
+                    ), '') AS comment
                     FROM pg_attribute a, pg_class c, pg_type t, pg_namespace n
                     WHERE " . $this->getTableWhereClause($table, 'c', 'n') . '
                         AND a.attnum > 0

lib/Doctrine/DBAL/Schema/PostgreSqlSchemaManager.php

@@ -440,14 +440,15 @@ protected function _getPortableTableColumnDefinition(array $tableColumn) : Colum
             'default'       => $tableColumn['default'],
             'precision'     => $precision,
             'scale'         => $scale,
-            'fixed'         => $fixed,
             'unsigned'      => false,
             'autoincrement' => $autoincrement,
-            'comment'       => isset($tableColumn['comment']) && $tableColumn['comment'] !== ''
-                ? $tableColumn['comment']
-                : null,
+            'comment'       => $tableColumn['comment'],
         ];
 
+        if ($fixed !== null) {
+            $options['fixed'] = $fixed;
+        }
+
         $column = new Column($tableColumn['field'], Type::getType($type), $options);
 
         if (isset($tableColumn['collation']) && ! empty($tableColumn['collation'])) {