Fixed mysql and mysqli drivers to set NOT NULL as default for creating fields. All other drivers were correct.
diff --git a/system/database/drivers/mysql/mysql_forge.php b/system/database/drivers/mysql/mysql_forge.php
index 529ec98..c1cae13 100644
--- a/system/database/drivers/mysql/mysql_forge.php
+++ b/system/database/drivers/mysql/mysql_forge.php
@@ -119,9 +119,13 @@
 					$sql .= ' DEFAULT \''.$attributes['DEFAULT'].'\'';
 				}
 
-				if (array_key_exists('NULL', $attributes))
+				if (array_key_exists('NULL', $attributes) && $attributes['NULL'] === TRUE)
 				{
-					$sql .= ($attributes['NULL'] === TRUE) ? ' NULL' : ' NOT NULL';
+					$sql .= ' NULL';
+				}
+				else
+				{
+					$sql .= ' NOT NULL';
 				}
 
 				if (array_key_exists('AUTO_INCREMENT', $attributes) && $attributes['AUTO_INCREMENT'] === TRUE)
diff --git a/system/database/drivers/mysqli/mysqli_forge.php b/system/database/drivers/mysqli/mysqli_forge.php
index d509733..2605494 100644
--- a/system/database/drivers/mysqli/mysqli_forge.php
+++ b/system/database/drivers/mysqli/mysqli_forge.php
@@ -104,9 +104,13 @@
 					$sql .= ' DEFAULT \''.$attributes['DEFAULT'].'\'';
 				}
 
-				if (array_key_exists('NULL', $attributes))
+				if (array_key_exists('NULL', $attributes) && $attributes['NULL'] === TRUE)
 				{
-					$sql .= ($attributes['NULL'] === TRUE) ? ' NULL' : ' NOT NULL';
+					$sql .= ' NULL';
+				}
+				else
+				{
+					$sql .= ' NOT NULL';
 				}
 
 				if (array_key_exists('AUTO_INCREMENT', $attributes) && $attributes['AUTO_INCREMENT'] === TRUE)