fix: nil check BatchHeader when reading JSON

Fixes: https://github.com/moov-io/ach/actions/runs/8841377405/job/24278386545

file.go

@@ -361,9 +361,10 @@ func (f *File) setBatchesFromJSON(bs []byte) error {
 	}
 	// Add new batches to file
 	for i := range batches.Batches {
-		if batches.Batches[i] == nil {
+		if batches.Batches[i] == nil || batches.Batches[i].Header == nil {
 			continue
 		}
+
 		batch := *batches.Batches[i]
 		batch.SetID(batch.Header.ID)
 		batch.SetValidation(f.validateOpts)
@@ -390,11 +391,12 @@ func (f *File) setBatchesFromJSON(bs []byte) error {
 
 	// Add new iatBatches to file
 	for i := range iatBatches.IATBatches {
-		if len(iatBatches.IATBatches) == 0 {
+		iatBatch := iatBatches.IATBatches[i]
+
+		if iatBatch.Header == nil {
 			continue
 		}
 
-		iatBatch := iatBatches.IATBatches[i]
 		iatBatch.ID = iatBatch.Header.ID
 		iatBatch.SetValidation(f.validateOpts)
 

server/test/unordered_batches/unordered_batch_test.go

@@ -52,7 +52,5 @@ func TestUnorderedBatches(t *testing.T) {
 	server.Handler.ServeHTTP(w, req)
 	w.Flush()
 
-	fmt.Printf("\n%s\n", w.Body.String())
-
 	require.Equal(t, http.StatusOK, w.Code)
 }

test/fuzz/testdata/fuzz/FuzzReaderWriterJSON/e499142d79b69666

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("{\"BAtChes\":[{\"BAtChHeAder\":null}]}")

test/fuzz/testdata/fuzz/FuzzReaderWriterJSON/iat-nil-header.txt

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("{\"iatBatches\":[{\"IATBatchHeader\":null}]}")