Update dependencies

@@ -127,6 +127,9 @@ class MyAppState extends State<MyApp> with SingleTickerProviderStateMixin {
     final bytes = await build(pageFormat);
 
     final appDocDir = await getApplicationDocumentsDirectory();
+    if (appDocDir == null) {
+      return;
+    }
     final appDocPath = appDocDir.path;
     final file = File(appDocPath + '/' + 'document.pdf');
     print('Save as file ${file.path} ...');

@@ -12,7 +12,7 @@ dependencies:
     sdk: flutter
   intl: ^0.17.0-nullsafety
   open_file:
-  path_provider:
+  path_provider: ^2.0.0-nullsafety
   printing:
   url_launcher: ^6.0.0-nullsafety
 

@@ -33,9 +33,10 @@ ffi.DynamicLibrary _open() {
 
 /// Set the Pdf document data
 void setDocumentFfi(PrintJob job, Uint8List data) {
-  final nativeBytes = ffi.allocate<ffi.Uint8>(count: data.length);
+  final nativeBytes = ffi.calloc<ffi.Uint8>(data.length);
   nativeBytes.asTypedList(data.length).setAll(0, data);
   _setDocument(job.index, nativeBytes, data.length);
+  ffi.calloc.free(nativeBytes);
 }
 
 final _SetDocument_Dart _setDocument =
@@ -57,7 +58,7 @@ typedef _SetDocument_Dart = void Function(
 
 /// Set the Pdf Error message
 void setErrorFfi(PrintJob job, String message) {
-  _setError(job.index, ffi.Utf8.toUtf8(message));
+  _setError(job.index, ffi.StringUtf8Pointer(message).toNativeUtf8());
 }
 
 final _SetError_Dart _setError =

@@ -11,7 +11,7 @@ environment:
   flutter: ">=1.16.0"
 
 dependencies:
-  ffi: ">=0.2.0-nullsafety <2.0.0"
+  ffi: ">=0.3.1-nullsafety.0 <2.0.0"
   flutter:
     sdk: flutter
   flutter_web_plugins: