Handling NULL in requests

[mickadoo]

Because of the way the database layer handles null values and string null we need to handle either string 'null' or true NULL input.

Since string 'null' is used to unset values it can't be used. When you pass true NULL as a value it will be ignored. To fix these problems this PR provides this workaround:

• If you set true NULL as a value it will be converted to string 'null' so the value will be unset
• If you set string 'null' as a value it will be converted to 'Null' since that's the only variation of string null that is allowed.