Prevent Potential Server Exception Viewing c-treeACE SQLExecution Plans

In examining reported server crashes, additional logic was added to the memory allocation and de-allocation routines in previous server builds. A NULL pointer could be generated through this new logic. While viewing an execution plan, it was noticed one of these NULL pointers could be de-referenced attempting to free the pointer resulting in a server crash. Additional checks on NULL pointers have been placed in the memory free routines to avoid this behavior.