Fix bug where ValueTransformer called with null. Fixes #804

Author: danvick

example/lib/sources/complete_form.dart

@@ -184,19 +184,20 @@ class CompleteFormState extends State<CompleteForm> {
                             ))
                         .toList(),
                     onChanged: (val) {
-                      print(val);
                       setState(() {
                         _genderHasError = !(_formKey
                                 .currentState?.fields['gender']
                                 ?.validate() ??
                             false);
                       });
                     },
+                    valueTransformer: (val) => val?.toString(),
                   ),
                   FormBuilderRadioGroup<String>(
                     decoration: const InputDecoration(
                       labelText: 'My chosen language',
                     ),
+                    initialValue: null,
                     name: 'best_language',
                     onChanged: _onChanged,
                     validator: FormBuilderValidators.compose(
@@ -238,7 +239,7 @@ class CompleteFormState extends State<CompleteForm> {
                     decoration: const InputDecoration(
                         labelText: 'The language of my people'),
                     name: 'languages',
-                    initialValue: const ['Dart'],
+                    // initialValue: const ['Dart'],
                     options: const [
                       FormBuilderFieldOption(value: 'Dart'),
                       FormBuilderFieldOption(value: 'Kotlin'),

lib/src/fields/form_builder_checkbox.dart

@@ -80,9 +80,9 @@ class FormBuilderCheckbox extends FormBuilderField<bool> {
       disabledBorder: InputBorder.none,
     ),
     ValueChanged<bool?>? onChanged,
-    ValueTransformer<bool>? valueTransformer,
+    ValueTransformer<bool?>? valueTransformer,
     bool enabled = true,
-    FormFieldSetter<bool>? onSaved,
+    FormFieldSetter<bool?>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,
     VoidCallback? onReset,
     FocusNode? focusNode,

lib/src/fields/form_builder_checkbox_group.dart

@@ -34,7 +34,7 @@ class FormBuilderCheckboxGroup<T> extends FormBuilderField<List<T>> {
     List<T>? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<List<T>?>? onChanged,
-    ValueTransformer<List<T>>? valueTransformer,
+    ValueTransformer<List<T>?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<List<T>>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_choice_chips.dart

@@ -248,7 +248,7 @@ class FormBuilderChoiceChip<T> extends FormBuilderField<T> {
     T? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<T?>? onChanged,
-    ValueTransformer<T>? valueTransformer,
+    ValueTransformer<T?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<T>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_date_range_picker.dart

@@ -69,7 +69,7 @@ class FormBuilderDateRangePicker extends FormBuilderField<DateTimeRange> {
     DateTimeRange? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<DateTimeRange?>? onChanged,
-    ValueTransformer<DateTimeRange>? valueTransformer,
+    ValueTransformer<DateTimeRange?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<DateTimeRange>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_date_time_picker.dart

@@ -136,7 +136,7 @@ class FormBuilderDateTimePicker extends FormBuilderField<DateTime> {
     DateTime? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<DateTime?>? onChanged,
-    ValueTransformer<DateTime>? valueTransformer,
+    ValueTransformer<DateTime?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<DateTime>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_dropdown.dart

@@ -190,7 +190,7 @@ class FormBuilderDropdown<T> extends FormBuilderField<T> {
     T? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<T?>? onChanged,
-    ValueTransformer<T>? valueTransformer,
+    ValueTransformer<T?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<T>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_filter_chips.dart

@@ -48,7 +48,7 @@ class FormBuilderFilterChip<T> extends FormBuilderField<List<T>> {
       disabledBorder: InputBorder.none,
     ),
     ValueChanged<List<T>?>? onChanged,
-    ValueTransformer<List<T>>? valueTransformer,
+    ValueTransformer<List<T>?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<List<T>>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_radio_group.dart

@@ -32,7 +32,7 @@ class FormBuilderRadioGroup<T> extends FormBuilderField<T> {
     T? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<T?>? onChanged,
-    ValueTransformer<T>? valueTransformer,
+    ValueTransformer<T?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<T>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,

lib/src/fields/form_builder_range_slider.dart

@@ -113,7 +113,7 @@ class FormBuilderRangeSlider extends FormBuilderField<RangeValues> {
     RangeValues? initialValue,
     InputDecoration decoration = const InputDecoration(),
     ValueChanged<RangeValues?>? onChanged,
-    ValueTransformer<RangeValues>? valueTransformer,
+    ValueTransformer<RangeValues?>? valueTransformer,
     bool enabled = true,
     FormFieldSetter<RangeValues>? onSaved,
     AutovalidateMode autovalidateMode = AutovalidateMode.disabled,