Error when `XHPROF_FLAGS_CPU` is removed from xhprof_enable configuration

[butschster]

Description

When configuring xhprof_enable with only XHPROF_FLAGS_MEMORY and omitting XHPROF_FLAGS_CPU, the application throws an error.

Error Message

{"message":"Undefined array key \"cpu\"","code":500}

Expected Behavior

The application should handle the absence of XHPROF_FLAGS_CPU without crashing, or provide a clear error message indicating the requirement.