fix the field of class assignment error

com.unity.uiwidgets/Runtime/material/pickers/calendar_date_picker.cs

             D.assert(initialDate != null);
             D.assert(firstDate != null);
             D.assert(lastDate != null);
-            initialDate = utils.dateOnly(initialDate.Value);
-            firstDate = utils.dateOnly(firstDate.Value);
-            lastDate = utils.dateOnly(lastDate.Value);
+            this.initialDate = utils.dateOnly(initialDate.Value);
+            this.firstDate = utils.dateOnly(firstDate.Value);
+            this.lastDate = utils.dateOnly(lastDate.Value);
             D.assert(onDateChanged != null);
             D.assert(initialCalendarMode != null);
 

Samples/UIWidgetsSamples_2019_4/Android/.idea/modules/Android.iml

+<?xml version="1.0" encoding="UTF-8"?>
+<module external.linked.project.id=":" external.linked.project.path="$MODULE_DIR$/../.." external.root.project.path="$MODULE_DIR$/../.." external.system.id="GRADLE" type="JAVA_MODULE" version="4">
+  <component name="FacetManager">
+    <facet type="android-gradle" name="Android-Gradle">
+      <configuration>
+        <option name="GRADLE_PROJECT_PATH" value=":" />
+        <option name="LAST_SUCCESSFUL_SYNC_AGP_VERSION" />
+        <option name="LAST_KNOWN_AGP_VERSION" />
+      </configuration>
+    </facet>
+  </component>
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$/../.." />
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>