How to disable to mark line as a comment (#) if it's blank

How to disable to make the line as a comment if the line is blank 
Suppose I have this things written, I select this lines and hit command + /, all line are marked as comment #.

a = 1

b = 3
c = 2

Result is

# a = 1
#
# b = 3
# c = 2

Expect result:

# a = 1

# b = 3
# c = 2