Bad variable reference syntax is an error.

In CMake 2.6.2 and below, incorrect variable reference syntax such as a missing close-brace (“${FOO”) was reported but did not stop processing of CMake code. This policy determines whether a bad variable reference is an error. The OLD behavior for this policy is to warn about the error, leave the string untouched, and continue. The NEW behavior for this policy is to report an error.

This policy was introduced in CMake version 2.6.3. CMake version 3.0.2 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.