gistfile1.coffee

# 1
data = if obj.data? then ("#{key}=#{value}" for key, value of obj.data).join "&" else null

# 2
data = if obj.data?
  ("#{key}=#{value}" for key, value of obj.data).join "&"
else
  null

# 3
data = if obj.data?
  (for own key, value of obj.data
    "#{key}=#{value}"
  ).join "&"
else
  null

# 4
data = ((("#{key}=#{value}" for key, value of obj.data).join "&" if obj.data?) ? null)

# 5
data = ("#{key}=#{value}" for key, value of obj.data).join "&" if obj.data?
data ?= null