Noissue - zero length OwnedString is valid.

compiled/String.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 277 matching lines @@
       mBuf = new value_type[length()];
       annotate_address(mBuf, "String");
     }
     else
       mBuf = nullptr;
   }
 
   explicit OwnedString(const String& str)
       : OwnedString(str.length())
   {
-    if (length())
+    if (!str.is_invalid() && !length())
+      mLen = length() | READ_WRITE;
+    else if (length())
       std::memcpy(mBuf, str.mBuf, sizeof(value_type) * length());
   }
 
   OwnedString(const OwnedString& str)
       : OwnedString(static_cast<const String&>(str))
   {
   }
 
   explicit OwnedString(const value_type* str, size_type len)
       : OwnedString(DependentString(str, len))
@@ skipping 102 matching lines @@
     if (negative)
       mBuf[pos++] = '-';
 
     for (int i = size - 1; i >= 0; i--)
     {
       mBuf[pos + i] = '0' + (num % 10);
       num /= 10;
     }
   }
 };