Catch date/time conversion errors in GetDateTimeValue, which happen e.g. when passing an empty date.

source/dbconnection.pas

@@ -3597,6 +3597,7 @@ begin
   // Return date/time string value as expected by server
   case Parameters.NetTypeGroup of
     ngMSSQL: begin
+      try
         dt := StrToDateTime(Input);
         case Datatype of
           dtDate:
@@ -3608,6 +3609,10 @@ begin
           dtDatetime:
             Result := SysUtils.FormatDateTime('dd"/"mm"/"yyyy hh":"nn":"ss', dt);
         end;
+      except
+        on E:EConvertError do
+          Result := Input;
+      end;
     end;
     else
       Result := Input;