Fix redact for environment ( or perhaps other provider ) variables that expand to empty string

[darach]

Expected Behavior

Given a configuration that users the .env provider with a configuration containing any
variable that mapss to the empty string

FOO=""

Redaction should ignore the variable.

Current Behavior

$ cat test.txt
This is a test
$ cat test.txt| teller redact
**REDACTED**T**REDACTED**h**REDACTED**i**REDACTED**s**REDACTED** **REDACTED**i**REDACTED**s**REDACTED** **REDACTED**a**REDACTED** **REDACTED**t**REDACTED**e**REDACTED**s**REDACTED**t**REDACTED**

Possible Solution

Preprocess and remove variables that expand to the empty string.

Steps to Reproduce

1. Create a .teller.yml with an env provider as above
2. Create a non empty test.txt file as above
3. Redact the file with teller
4. Every character will contain an unwanted **REDACTED**

Context

Ideally, environment variables should not expand to the empty string - but this will not always be practicable or possible

Specifications

• Version: $ teller version

Teller 1.5.6
Revision 7b714bc2f1d5e14920f2add828fdf7425148ff6b, date: 2022-10-13T08:02:44Z

• Platform:

 uname -a | teller redact
Darwin **REDACTED** 22.6.0 Darwin Kernel Version 22.6.0: Wed Oct  4 21:25:26 PDT 2023; root:xnu-8796.141.3.701.17~4/RELEASE_X86_64 x86_64

[jondot]

Thanks, should be fixed with Teller 2.0 now.