Making mass/bulk update by attribute value in ArcGIS Desktop?

I have feature class with 70,000+ records (file geodatabase). I want to make in bulk update on an attribute where the value is NULL. Select by attribute shows that I have 5,000 records like that. Doing it one by one is going to be a pain.

In sql pseudo code it should be something like that:

 UPDATE  = 'NewValue'
 WHERE  IS NULL

How do I do that with ArcMap 10.1?

Answer

You would select the rows which are NULL (sounds like you have done that) then simply run the calculate field tool.

Right Click the field you want to modify (while objects are selected)

Then input your value "newvalue"

NOTE: 1. if you don't have a selection this will work on "ALL" rows in your table!
2. Double quotes in this area on your text/date value. See esri help for examples of vba/python/string/number/codeblock options
3. Must begin edit session to run in FGDB.