#701 - DB Migration - incorrect alter column DDL when removing not null constraint (Postgres specific)

src/main/java/com/avaje/ebean/dbmigration/ddlgeneration/platform/PostgresDdl.java

@@ -13,6 +13,7 @@ public class PostgresDdl extends PlatformDdl {
     this.dropTableCascade = " cascade";
     this.columnSetType = "type ";
     this.alterTableIfExists = "if exists ";
+    this.columnSetNull = "drop not null";
   }
 
   /**

src/test/java/com/avaje/ebean/dbmigration/ddlgeneration/platform/PlatformDdl_AlterColumnTest.java

@@ -103,7 +103,7 @@ public class PlatformDdl_AlterColumnTest {
     assertEquals("alter table mytab alter column acol set null", sql);
 
     sql = pgDdl.alterColumnNotnull("mytab", "acol", false);
-    assertEquals("alter table mytab alter column acol set null", sql);
+    assertEquals("alter table mytab alter column acol drop not null", sql);
 
     sql = oraDdl.alterColumnNotnull("mytab", "acol", false);
     assertEquals("alter table mytab modify acol null", sql);