Fix bug in AST (zio#223)

* Fix bug in AST

* Remove unused import

Author: thinkharderdev

tests/shared/src/test/scala/zio/schema/SchemaAstSpec.scala

@@ -210,6 +210,11 @@ object SchemaAstSpec extends DefaultRunnableSpec {
         val schema       = Schema[List[Option[Int]]]
         val materialized = SchemaAst.fromSchema(schema).toSchema
         assert(materialized)(hasSameSchemaStructure(schema))
+      },
+      test("optional sequence of primitives") {
+        val schema       = Schema[Option[List[String]]]
+        val materialized = SchemaAst.fromSchema(schema).toSchema
+        assert(materialized)(hasSameSchemaStructure(schema))
       }
     )
   )

zio-schema/shared/src/main/scala/zio/schema/ast/SchemaAst.scala

@@ -338,7 +338,7 @@ object SchemaAst {
               optional
             )
           case Schema.Sequence(schema, _, _, _, _) =>
-            ListNode(item = subtree(path / "item", lineage, schema, optional), path)
+            ListNode(item = subtree(path / "item", lineage, schema, optional = false), path, optional)
           case Schema.MapSchema(ks, vs, _) =>
             Dictionary(
               keys = subtree(path / "keys", Chunk.empty, ks, optional = false),
@@ -347,7 +347,7 @@ object SchemaAst {
               optional
             )
           case Schema.SetSchema(schema @ _, _) =>
-            ListNode(item = subtree(path / "item", lineage, schema, optional), path)
+            ListNode(item = subtree(path / "item", lineage, schema, optional = false), path, optional)
           case Schema.Transform(schema, _, _, _, _) => subtree(path, lineage, schema, optional)
           case lzy @ Schema.Lazy(_)                 => subtree(path, lineage, lzy.schema, optional)
           case s: Schema.Record[_] =>