idlwave-complete-empty-string-as-lower-case

idlwave-complete-empty-string-as-lower-case is a variable defined in `idlwave.el'.
Its value is

nil

Documentation:
Non-nil means, the empty string is considered downcase for completion.
The case of what is already in the buffer determines the case of completions.
When this variable is non-nil, the empty string is considered to be downcase.
Completing on the empty string then offers downcase versions of the possible
completions.

You can customize this variable.