Nullable columns now output NULL DEFAULT NULL in DDL

When a column is nullable and no explicit default is set, the generated
SQL now includes NULL DEFAULT NULL instead of omitting both keywords.
Fixes #140.

Signed-off-by: Simon Mundy <[email protected]>

Author: simon-mundy

src/Sql/Ddl/Column/Column.php

@@ -115,13 +115,17 @@ public function getExpressionData(): array
 
         if ($this->isNullable === false) {
             $specParts[] = 'NOT NULL';
+        } else {
+            $specParts[] = 'NULL';
         }
 
         if ($this->default !== null) {
             $specParts[] = 'DEFAULT %s';
             $values[]    = $this->default instanceof ArgumentInterface
                 ? $this->default
                 : new Value($this->default);
+        } elseif ($this->isNullable) {
+            $specParts[] = 'DEFAULT NULL';
         }
 
         foreach ($this->constraints as $constraint) {

test/unit/Sql/Ddl/Column/ColumnTest.php

@@ -151,7 +151,7 @@ public function testGetExpressionData(): void
 
         $expressionData = $column->getExpressionData();
 
-        self::assertEquals('%s %s', $expressionData['spec']);
+        self::assertEquals('%s %s NULL DEFAULT NULL', $expressionData['spec']);
         self::assertEquals([
             Argument::identifier('foo'),
             Argument::literal('INTEGER'),
@@ -161,7 +161,7 @@ public function testGetExpressionData(): void
 
         $expressionData = $column->getExpressionData();
 
-        self::assertEquals('%s %s DEFAULT %s', $expressionData['spec']);
+        self::assertEquals('%s %s NULL DEFAULT %s', $expressionData['spec']);
         self::assertEquals([
             Argument::identifier('foo'),
             Argument::literal('INTEGER'),