Auto compute in date format issue

[daw7]

Situation:

• I have my first column named [Date A] in date format. This is where I input my data.
• I got another column named [Date B] in date format, with auto compute formula of “[Date A] + 30”
• My intention is to show that column [Date B] is 1 month (or 30 days) ahead of column [Date A]
• column [Date A] has no initial value since this is where I want to input my data
• column [Date B] has no initial value also since it already contains an auto compute formula

Issue

• Even if column [Date A] has no data input yet, column [Date B] will show a value of “01/31/1970”
• I tried putting an initial value on column [Date B] of " " which basically what I want is to show a blank value initially, but my app displayed an error message "Value ‘NaN/NaN/0NaN’ in field ‘Date B’ cannot be converted to type ‘Date’.

Please help. Thank you!