fix: Fix npe in pagination (backport #23880) (#23883)

Co-authored-by: Eric Warehime <eric.warehime@gmail.com>
Co-authored-by: aljo242 <alex@interchainlabs.io>

CHANGELOG.md

@@ -51,6 +51,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Bug Fixes
 
+* (query) [#23883](https://github.com/cosmos/cosmos-sdk/pull/23883) Fix NPE in query pagination.
 * (client) [#23860](https://github.com/cosmos/cosmos-sdk/pull/23860) Add missing `unordered` field for legacy amino signing of tx body.
 * (x/bank) [#23836](https://github.com/cosmos/cosmos-sdk/pull/23836) Fix `DenomMetadata` rpc allow value with slashes.
 * (query) [87d3a43](https://github.com/cosmos/cosmos-sdk/commit/87d3a432af95f4cf96aa02351ed5fcc51cca6e7b) Fix collection filtered pagination.

types/query/collections_pagination.go

@@ -104,7 +104,7 @@ func CollectionFilteredPaginate[K, V any, C Collection[K, V], T any](
 		return results, new(PageResponse), nil
 	}
 	// strip the prefix from next key
-	if len(pageRes.NextKey) != 0 && prefix != nil {
+	if pageRes != nil && len(pageRes.NextKey) != 0 && prefix != nil {
 		pageRes.NextKey = pageRes.NextKey[len(prefix):]
 	}
 	return results, pageRes, err

types/query/collections_pagination_test.go

@@ -2,6 +2,7 @@ package query
 
 import (
 	"context"
+	"errors"
 	"testing"
 
 	db "github.com/cosmos/cosmos-db"
@@ -15,6 +16,7 @@ func TestCollectionPagination(t *testing.T) {
 	sk, ctx := deps()
 	sb := collections.NewSchemaBuilder(sk)
 	m := collections.NewMap(sb, collections.NewPrefix(0), "_", collections.Uint64Key, collections.Uint64Value)
+	dummyErr := errors.New("dummy error")
 
 	for i := uint64(0); i < 300; i++ {
 		require.NoError(t, m.Set(ctx, i, i))
@@ -152,6 +154,18 @@ func TestCollectionPagination(t *testing.T) {
 				{Key: 295, Value: 295},
 			},
 		},
+		"filtered no key with error": {
+			req: &PageRequest{
+				Limit: 3,
+			},
+			expResp: &PageResponse{
+				NextKey: encodeKey(5),
+			},
+			filter: func(key, value uint64) (bool, error) {
+				return false, dummyErr
+			},
+			wantErr: dummyErr,
+		},
 	}
 
 	for name, tc := range tcs {