[MaterialDatePicker] Improve inputs validation

PiperOrigin-RevId: 489269023

lib/java/com/google/android/material/datepicker/CalendarConstraints.java

@@ -27,6 +27,7 @@
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.util.Arrays;
 import java.util.Calendar;
+import java.util.Objects;
 
 /**
  * Used to limit the display range of the calendar and set an openAt month.
@@ -64,6 +65,9 @@ private CalendarConstraints(
       @NonNull DateValidator validator,
       @Nullable Month openAt,
       int firstDayOfWeek) {
+    Objects.requireNonNull(start, "start cannot be null");
+    Objects.requireNonNull(end, "end cannot be null");
+    Objects.requireNonNull(validator, "validator cannot be null");
     this.start = start;
     this.end = end;
     this.openAt = openAt;
@@ -370,6 +374,7 @@ public Builder setFirstDayOfWeek(int firstDayOfWeek) {
     @NonNull
     @CanIgnoreReturnValue
     public Builder setValidator(@NonNull DateValidator validator) {
+      Objects.requireNonNull(validator, "validator cannot be null");
       this.validator = validator;
       return this;
     }