found the soundness hole

src/impls.rs

@@ -6,6 +6,7 @@ use std::{
     fmt::Debug,
     mem::size_of,
     ops::{Deref, DerefMut},
+    ptr::NonNull,
     slice,
     vec::Vec as StdVec,
 };
@@ -161,15 +162,23 @@ impl<T> Deref for Vec<T> {
     type Target = [T];
 
     fn deref(&self) -> &Self::Target {
+        if self.is_empty() {
+            unsafe { slice::from_raw_parts(NonNull::dangling().as_ptr(), 0) }
+        } else {
             unsafe { slice::from_raw_parts(self.get_ptr(0), self.len) }
         }
     }
+}
 
 impl<T> DerefMut for Vec<T> {
     fn deref_mut(&mut self) -> &mut Self::Target {
+        if self.is_empty() {
+            unsafe { slice::from_raw_parts_mut(NonNull::dangling().as_ptr(), 0) }
+        } else {
             unsafe { slice::from_raw_parts_mut(self.get_ptr(0) as _, self.len) }
         }
     }
+}
 
 unsafe impl<T: Send> Send for Vec<T> {}
 unsafe impl<T: Sync> Sync for Vec<T> {}