Update Conversion.cs (#5627)

Author: 4201104140

src/Microsoft.ML.Data/Data/Conversion.cs

@@ -950,8 +950,8 @@ public void Convert(in BL src, ref SB dst)
         public void Convert(in R8 src, ref TX dst) => dst = src.ToString("G17", CultureInfo.InvariantCulture).AsMemory();
         public void Convert(in BL src, ref TX dst) => dst = src.ToString().AsMemory();
         public void Convert(in TS src, ref TX dst) => dst = string.Format("{0:c}", src).AsMemory();
-        public void Convert(in DT src, ref TX dst) => string.Format("{0:o}", src).AsMemory();
-        public void Convert(in DZ src, ref TX dst) => string.Format("{0:o}", src).AsMemory();
+        public void Convert(in DT src, ref TX dst) => dst = string.Format("{0:o}", src).AsMemory();
+        public void Convert(in DZ src, ref TX dst) => dst = string.Format("{0:o}", src).AsMemory();
         #endregion ToTX
 
         #region ToBL
@@ -1733,4 +1733,4 @@ public void Convert(in TX src, ref SB dst)
         public void Convert(in DT src, ref DT dst) => dst = src;
         #endregion ToDT
     }
-}
+}