Improve internal null-safety

 # Changelog
 
+## 3.0.1
+
+- Improve internal null-safety
+
 ## 3.0.0
 
 - Fix Checkbox Widget

@@ -123,7 +123,7 @@ abstract class PdfAnnotBase {
   /// Color
   final PdfColor? color;
 
-  final Map<String?, PdfDataType> _appearances = <String?, PdfDataType>{};
+  final Map<String, PdfDataType> _appearances = <String, PdfDataType>{};
 
   PdfName? _as;
 
@@ -231,7 +231,7 @@ abstract class PdfAnnotBase {
     if (_appearances.isNotEmpty) {
       params['/AP'] = PdfDict(_appearances);
       if (_as != null) {
-        params['/AS'] = _as;
+        params['/AS'] = _as!;
       }
     }
   }

@@ -158,7 +158,7 @@ class PdfString extends PdfDataType {
     return PdfString(_date(date));
   }
 
-  final Uint8List? value;
+  final Uint8List value;
 
   final PdfStringFormat format;
 
@@ -269,11 +269,11 @@ class PdfString extends PdfDataType {
   int _codeUnitForDigit(int digit) =>
       digit < 10 ? digit + 0x30 : digit + 0x61 - 10;
 
-  void _output(PdfStream s, Uint8List? value) {
+  void _output(PdfStream s, Uint8List value) {
     switch (format) {
       case PdfStringFormat.binary:
         s.putByte(0x3c);
-        for (var byte in value!) {
+        for (var byte in value) {
           s.putByte(_codeUnitForDigit((byte & 0xF0) >> 4));
           s.putByte(_codeUnitForDigit(byte & 0x0F));
         }
@@ -281,7 +281,7 @@ class PdfString extends PdfDataType {
         break;
       case PdfStringFormat.litteral:
         s.putByte(40);
-        _putTextBytes(s, value!);
+        _putTextBytes(s, value);
         s.putByte(41);
         break;
     }
@@ -350,7 +350,7 @@ class PdfSecString extends PdfString {
       return super.output(s);
     }
 
-    final enc = object.pdfDocument.encryption!.encrypt(value!, object);
+    final enc = object.pdfDocument.encryption!.encrypt(value, object);
     _output(s, enc);
   }
 }
@@ -457,9 +457,9 @@ class PdfArray extends PdfDataType {
     return PdfArray(list.map<PdfNum>((num? e) => PdfNum(e!)).toList());
   }
 
-  final List<PdfDataType?> values = <PdfDataType?>[];
+  final List<PdfDataType> values = <PdfDataType>[];
 
-  void add(PdfDataType? v) {
+  void add(PdfDataType v) {
     values.add(v);
   }
 
@@ -468,7 +468,7 @@ class PdfArray extends PdfDataType {
     s.putString('[');
     if (values.isNotEmpty) {
       for (var n = 0; n < values.length; n++) {
-        final val = values[n]!;
+        final val = values[n];
         if (n > 0 &&
             !(val is PdfName ||
                 val is PdfString ||
@@ -489,7 +489,7 @@ class PdfArray extends PdfDataType {
     }
 
     // ignore: prefer_collection_literals
-    final uniques = LinkedHashMap<PdfDataType?, bool>();
+    final uniques = LinkedHashMap<PdfDataType, bool>();
     for (final s in values) {
       uniques[s] = true;
     }
@@ -511,7 +511,7 @@ class PdfArray extends PdfDataType {
 }
 
 class PdfDict extends PdfDataType {
-  PdfDict([Map<String?, PdfDataType>? values]) {
+  PdfDict([Map<String, PdfDataType>? values]) {
     if (values != null) {
       this.values.addAll(values);
     }
@@ -526,27 +526,27 @@ class PdfDict extends PdfDataType {
     );
   }
 
-  final Map<String?, PdfDataType?> values = <String?, PdfDataType?>{};
+  final Map<String, PdfDataType> values = <String, PdfDataType>{};
 
   bool get isNotEmpty => values.isNotEmpty;
 
-  operator []=(String k, PdfDataType? v) {
+  operator []=(String k, PdfDataType v) {
     values[k] = v;
   }
 
-  PdfDataType? operator [](String? k) {
+  PdfDataType? operator [](String k) {
     return values[k];
   }
 
   @override
   void output(PdfStream s) {
     s.putBytes(const <int>[0x3c, 0x3c]);
-    values.forEach((String? k, PdfDataType? v) {
+    values.forEach((String k, PdfDataType v) {
       s.putString(k);
       if (v is PdfNum || v is PdfBool || v is PdfNull || v is PdfIndirect) {
         s.putByte(0x20);
       }
-      v!.output(s);
+      v.output(s);
     });
     s.putBytes(const <int>[0x3e, 0x3e]);
   }
@@ -557,7 +557,7 @@ class PdfDict extends PdfDataType {
 
   void merge(PdfDict other) {
     for (final key in other.values.keys) {
-      final value = other[key];
+      final value = other[key]!;
       final current = values[key];
       if (current == null) {
         values[key] = value;

@@ -147,7 +147,7 @@ class PdfDocument {
   Uint8List? _documentID;
 
   /// Generates the document ID
-  Uint8List? get documentID {
+  Uint8List get documentID {
     if (_documentID == null) {
       final rnd = math.Random();
       _documentID = Uint8List.fromList(sha256
@@ -156,7 +156,7 @@ class PdfDocument {
           .bytes);
     }
 
-    return _documentID;
+    return _documentID!;
   }
 
   /// Creates a new serial number
@@ -169,18 +169,18 @@ class PdfDocument {
   }
 
   /// The root outline
-  PdfOutline? get outline {
+  PdfOutline get outline {
     if (_outline == null) {
       _outline = PdfOutline(this);
       catalog.outlines = _outline;
     }
-    return _outline;
+    return _outline!;
   }
 
   /// Graphic states for opacity and transfer modes
-  PdfGraphicStates? get graphicStates {
+  PdfGraphicStates get graphicStates {
     _graphicStates ??= PdfGraphicStates(this);
-    return _graphicStates;
+    return _graphicStates!;
   }
 
   /// This document has at least one graphic state

@@ -88,7 +88,7 @@ mixin PdfGraphicStream on PdfObject {
 
   /// Generate a name for the graphic state object
   String stateName(PdfGraphicState state) {
-    return pdfDocument.graphicStates!.stateName(state);
+    return pdfDocument.graphicStates.stateName(state);
   }
 
   @override
@@ -135,7 +135,7 @@ mixin PdfGraphicStream on PdfObject {
         '/K': PdfBool(knockoutTransparency),
       });
 
-      resources['/ExtGState'] = pdfDocument.graphicStates!.ref();
+      resources['/ExtGState'] = pdfDocument.graphicStates.ref();
     }
 
     if (params.containsKey('/Resources')) {

@@ -57,7 +57,7 @@ class PdfNames extends PdfObject {
 
     for (var name in keys) {
       dests.add(PdfSecString.fromString(this, name));
-      dests.add(_dests[name]);
+      dests.add(_dests[name]!);
     }
 
     final dict = PdfDict();

@@ -80,7 +80,7 @@ class PdfPage extends PdfObject with PdfGraphicStream {
       final contentList = PdfArray.fromObjects(contents);
 
       if (params.containsKey('/Contents')) {
-        final prevContent = params['/Contents'];
+        final prevContent = params['/Contents']!;
         if (prevContent is PdfArray) {
           contentList.values.insertAll(0, prevContent.values);
         } else {

@@ -337,7 +337,7 @@ class Outline extends Anchor {
     var l = level;
 
     while (l > 0) {
-      if (parent!.effectiveLevel == l) {
+      if (parent.effectiveLevel == l) {
         break;
       }
 
@@ -349,6 +349,6 @@ class Outline extends Anchor {
       l--;
     }
 
-    parent!.add(_outline!);
+    parent.add(_outline!);
   }
 }

@@ -4,7 +4,7 @@ description: A pdf producer for Dart. It can create pdf files for both web or fl
 homepage: https://github.com/DavBfr/dart_pdf/tree/master/pdf
 repository: https://github.com/DavBfr/dart_pdf
 issue_tracker: https://github.com/DavBfr/dart_pdf/issues
-version: 3.0.0
+version: 3.0.1
 
 environment:
   sdk: ">=2.12.0-0 <3.0.0"