diff --git a/storage/sql.go b/storage/sql.go
index c9b36ec..7722099 100644
--- a/storage/sql.go
+++ b/storage/sql.go
@@ -214,8 +214,7 @@ func (s *SQLAdapter) GetContext(ctx context.Context, dest any, filter map[string
 	if len(filter) == 0 {
 		return errors.New("filtering is required when getting a resource")
 	}
-	query, bindings := s.buildQuery(filter)
-	result := s.dbWithCtx(ctx).Where(query, bindings).Find(dest)
+	result := s.applyFilter(s.dbWithCtx(ctx), filter).Find(dest)
 	if result.RowsAffected == 0 {
 		return ErrNotFound
 	}
@@ -230,8 +229,7 @@ func (s *SQLAdapter) UpdateContext(ctx context.Context, item any, filter map[str
 	if len(filter) == 0 {
 		return errors.New("filtering is required when updating a resource")
 	}
-	query, bindings := s.buildQuery(filter)
-	result := s.dbWithCtx(ctx).Where(query, bindings).Save(item)
+	result := s.applyFilter(s.dbWithCtx(ctx), filter).Save(item)
 	return result.Error
 }
 
@@ -243,8 +241,7 @@ func (s *SQLAdapter) DeleteContext(ctx context.Context, item any, filter map[str
 	if len(filter) == 0 {
 		return errors.New("filtering is required when deleting a resource")
 	}
-	query, bindings := s.buildQuery(filter)
-	result := s.dbWithCtx(ctx).Where(query, bindings).Delete(item)
+	result := s.applyFilter(s.dbWithCtx(ctx), filter).Delete(item)
 	return result.Error
 }
 
@@ -342,8 +339,7 @@ func (s *SQLAdapter) ListContext(ctx context.Context, dest any, sortKey string,
 	}
 	return s.executePaginatedQuery(ctx, dest, sortKey, sortDirection, limit, cursor, func(q *gorm.DB) *gorm.DB {
 		if len(filter) > 0 {
-			query, bindings := s.buildQuery(filter)
-			return q.Where(query, bindings)
+			return s.applyFilter(q, filter)
 		}
 		return q
 	})
@@ -402,8 +398,7 @@ func (s *SQLAdapter) CountContext(ctx context.Context, dest any, filter map[stri
 	q := s.dbWithCtx(ctx).Model(dest)
 
 	if len(filter) > 0 {
-		query, bindings := s.buildQuery(filter)
-		q = q.Where(query, bindings)
+		q = s.applyFilter(q, filter)
 	}
 
 	var total int64
@@ -414,6 +409,21 @@ func (s *SQLAdapter) CountContext(ctx context.Context, dest any, filter map[stri
 	return total, nil
 }
 
+// applyFilter builds a WHERE clause from the filter map and attaches it to
+// the given gorm session. When the bindings map is empty (e.g. a filter like
+// {"deleted_at": nil} which produces only an "IS NULL" clause) we must NOT
+// forward an empty map[string]any{} as a parameter to GORM — pgx5 in
+// PreferSimpleProtocol mode cannot encode it and fails with
+// "unable to encode map[string]interface{}{} into text format for unknown
+// type (OID 0): cannot find encode plan". Pass the query alone instead.
+func (s *SQLAdapter) applyFilter(q *gorm.DB, filter map[string]any) *gorm.DB {
+	query, bindings := s.buildQuery(filter)
+	if len(bindings) == 0 {
+		return q.Where(query)
+	}
+	return q.Where(query, bindings)
+}
+
 func (s *SQLAdapter) Query(dest any, statement string, limit int, cursor string, params ...map[string]any) (string, error) {
 	return s.QueryContext(context.Background(), dest, statement, limit, cursor, params...)
 }
diff --git a/storage/sql_test.go b/storage/sql_test.go
index d266e2e..ae92207 100644
--- a/storage/sql_test.go
+++ b/storage/sql_test.go
@@ -302,3 +302,68 @@ func TestMemoryAdapterDelegatesNonContextCountAndQuery(t *testing.T) {
 		t.Fatalf("expected memory.Query to propagate not-implemented error")
 	}
 }
+
+// nilFilterItem has a nullable column so we can build filters whose
+// only entry has a nil value, exercising buildQuery's IS NULL branch.
+type nilFilterItem struct {
+	Id        string  `json:"id" gorm:"primaryKey;column:id"`
+	DeletedAt *string `json:"deleted_at" gorm:"column:deleted_at"`
+}
+
+func (nilFilterItem) TableName() string { return "nil_filter_items" }
+
+// TestSQLAdapterNilOnlyFilterDoesNotForwardEmptyBindings pins the fix
+// for the pgx5 simple-protocol crash where buildQuery returned an empty
+// map[string]any{} as bindings for nil-only filters and gorm forwarded
+// it to pgx as a parameter ("unable to encode map[string]interface{}{}
+// into text format for unknown type (OID 0): cannot find encode plan").
+//
+// applyFilter must call q.Where(query) with NO variadic args when
+// bindings are empty. Sqlite tolerates the broken shape, so this test
+// exercises behavioral correctness (nil-only filters return the right
+// rows) — if a future cleanup reintroduces empty-map forwarding, this
+// keeps passing under sqlite but the matching pgx5 path will regress.
+// The unit invariant we lock in here is "Count/Get/List with a nil-only
+// filter return the expected rows without error".
+func TestSQLAdapterNilOnlyFilterDoesNotForwardEmptyBindings(t *testing.T) {
+	m := storage.GetMemoryAdapterInstance()
+	if err := m.Execute(`CREATE TABLE IF NOT EXISTS nil_filter_items (id TEXT PRIMARY KEY, deleted_at TEXT)`); err != nil {
+		t.Fatalf("create table: %v", err)
+	}
+	if err := m.Execute(`DELETE FROM nil_filter_items`); err != nil {
+		t.Fatalf("truncate: %v", err)
+	}
+	sql := m.DB
+
+	if err := sql.Create(&nilFilterItem{Id: "live"}); err != nil {
+		t.Fatalf("Create live: %v", err)
+	}
+	deletedTs := "2026-01-01"
+	if err := sql.Create(&nilFilterItem{Id: "gone", DeletedAt: &deletedTs}); err != nil {
+		t.Fatalf("Create gone: %v", err)
+	}
+
+	total, err := sql.Count(&[]nilFilterItem{}, map[string]any{"deleted_at": nil})
+	if err != nil {
+		t.Fatalf("Count with nil-only filter: %v", err)
+	}
+	if total != 1 {
+		t.Fatalf("Count = %d; want 1 (only the non-deleted row)", total)
+	}
+
+	var got nilFilterItem
+	if err := sql.Get(&got, map[string]any{"deleted_at": nil}); err != nil {
+		t.Fatalf("Get with nil-only filter: %v", err)
+	}
+	if got.Id != "live" {
+		t.Fatalf("Get id = %q; want %q", got.Id, "live")
+	}
+
+	var listed []nilFilterItem
+	if _, err := sql.List(&listed, "id", map[string]any{"deleted_at": nil}, 10, ""); err != nil {
+		t.Fatalf("List with nil-only filter: %v", err)
+	}
+	if len(listed) != 1 || listed[0].Id != "live" {
+		t.Fatalf("List = %+v; want one row id=live", listed)
+	}
+}