Confirm that FormBuilderState is not null before trying to send field value

Author: danvick

lib/src/form_builder_field.dart

@@ -116,12 +116,14 @@ class FormBuilderFieldState<T> extends FormFieldState<T> with AfterInitMixin {
   @override
   void save() {
     super.save();
-    if (!_formBuilderState.widget.skipReadOnly ||
-        (_formBuilderState.widget.skipReadOnly && !readOnly)) {
-      _formBuilderState?.setInternalFieldValue(
-          widget.name, widget.valueTransformer?.call(value) ?? value);
-    } else {
-      _formBuilderState?.removeInternalFieldValue(widget.name);
+    if (_formBuilderState != null) {
+      if (!_formBuilderState.widget.skipReadOnly ||
+          (_formBuilderState.widget.skipReadOnly && !readOnly)) {
+        _formBuilderState.setInternalFieldValue(
+            widget.name, widget.valueTransformer?.call(value) ?? value);
+      } else {
+        _formBuilderState.removeInternalFieldValue(widget.name);
+      }
     }
   }