# CMP0102

New in version 3.17.

The `mark_as_advanced()` command no longer creates a cache entry if one does not already exist.

In CMake 3.16 and below, if a variable was not defined at all or just defined locally, the `mark_as_advanced()` command would create a new cache entry with an `UNINITIALIZED` type and no value. When a `find_path()` (or other similar `find_` command) would next run, it would find this undefined cache entry and set it up with an empty string value. This process would end up deleting the local variable in the process (due to the way the cache works), effectively clearing any stored `find_` results that were only available in the local scope.

The `OLD` behavior for this policy is to create the empty cache definition. The `NEW` behavior of this policy is to ignore variables which do not already exist in the cache.

This policy was introduced in CMake version 3.17. Use the `cmake_policy()` command to set it to `OLD` or `NEW` explicitly. Unlike many policies, CMake version 3.19.0-rc1 does not warn when this policy is not set and simply uses `OLD` behavior.

Note

The `OLD` behavior of a policy is `deprecated by definition` and may be removed in a future version of CMake.