ImageProvider.resolve returns non-null object

@@ -7,6 +7,7 @@
 - Add individual cell decoration
 - Improve Bullet Widget
 - Use covariant on SpanningWidget
+- ImageProvider.resolve returns non-null object
 
 ## 3.2.0
 

@@ -53,7 +53,7 @@ class DecorationImage extends DecorationGraphic {
 
   @override
   void paint(Context context, PdfRect box) {
-    final _image = image.resolve(context, box.size, dpi: dpi)!;
+    final _image = image.resolve(context, box.size, dpi: dpi);
 
     final imageSize =
         PdfPoint(_image.width.toDouble(), _image.height.toDouble());

@@ -121,7 +121,7 @@ class Image extends Widget {
 
     _paintImage(
       canvas: context.canvas,
-      image: image.resolve(context, rect.size, dpi: dpi)!,
+      image: image.resolve(context, rect.size, dpi: dpi),
       rect: box!,
       alignment: alignment,
       fit: fit,

@@ -51,7 +51,7 @@ abstract class ImageProvider {
 
   /// Resolves this image provider using the given context, returning a PdfImage
   /// The image is automatically added to the document
-  PdfImage? resolve(Context context, PdfPoint size, {double? dpi}) {
+  PdfImage resolve(Context context, PdfPoint size, {double? dpi}) {
     final effectiveDpi = dpi ?? this.dpi;
 
     if (effectiveDpi == null || _cache[0] != null) {
@@ -59,7 +59,7 @@ abstract class ImageProvider {
 
       assert(_cache[0]!.pdfDocument == context.document,
           'Do not reuse an ImageProvider object across multiple documents');
-      return _cache[0];
+      return _cache[0]!;
     }
 
     final width = (size.x / PdfPageFormat.inch * effectiveDpi).toInt();
@@ -71,7 +71,7 @@ abstract class ImageProvider {
 
     assert(_cache[width]!.pdfDocument == context.document,
         'Do not reuse an ImageProvider object across multiple documents');
-    return _cache[width];
+    return _cache[width]!;
   }
 }