What's difference between an empty string and a null value

Question: What is the difference between an "empty" value and a "null" value? 
Answer: An empty string is treated as a null value in Oracle.

Demo
NIGT013.COLL_B_DATE is null, and apply NVL2 to  substitute a value (i.e. empty string) when a null value is encountered.

But it showed null value in report. It results from an empty string is treated as a null value in Oracle

Therefore, in order to show non-null value in my report. Substitute two spaces when a null value is encountered.

Then it won't show null value in report anymore.

7 Application Deployment Best Practices

1. Keep the installation structure SIMPLE. 
2. Always get rid of old files. 
3. Automate it 
4. Don’t over do it with the symlinks
5. Delete everything first. 
6. Have a roll back strategy.
7. Don’t make changes to your deploy mechanism or deploy scripts between deploying to different environments. 

http://java.dzone.com/articles/7-application-deployment-best

Top 7 programmers bad habits

1. The all code is crap, except mine, attitude.
2. The “I fix that in a second” catastrophe.
3. The “That will only take a second” misconception.
4. The ego spiral.
5. “It wasn’t me!”
6. The demotivated genius.
7. The premature programmer.

http://www.dzone.com/links/r/top_7_programmers_bad_habits.html