Error importing data when open/close hour column fields value is 0

[pmallol]

version: 0.3.2-dev-631e732 (build 418)

1. Go to https://aslm1-stg.instedd.org/datasets
2. Login
3. Inside the ONA tab, drag and drop your local data.csv file on top of the "data.csv" square and wait for it to upload
4. Click on IMPORT button

Obtained:
The following error:

I, [2019-01-21T18:15:05.004937 #5222]  INFO -- : Generating facilities.csv file
/app/app/models/convert_from_ona.rb:92:in `get_hours': undefined method `slice' for 0:Fixnum (NoMethodError)
	from /app/app/models/convert_from_ona.rb:61:in `get_opening_hours'
	from /app/app/models/convert_from_ona.rb:56:in `block in get_opening_hours_array'
	from /app/app/models/convert_from_ona.rb:56:in `map'
	from /app/app/models/convert_from_ona.rb:56:in `get_opening_hours_array'
	from /app/app/models/convert_from_ona.rb:43:in `block in convert'
	from /app/app/models/convert_from_ona.rb:120:in `<<'
	from /app/app/models/convert_from_ona.rb:120:in `block (2 levels) in csv_enumerator'
	from /usr/local/lib/ruby/2.3.0/csv.rb:1748:in `each'
	from /usr/local/lib/ruby/2.3.0/csv.rb:1131:in `block in foreach'
	from /usr/local/lib/ruby/2.3.0/csv.rb:1282:in `open'
	from /usr/local/lib/ruby/2.3.0/csv.rb:1130:in `foreach'
	from /app/app/models/convert_from_ona.rb:119:in `block in csv_enumerator'
	from /app/app/models/convert_from_ona.rb:30:in `each'
	from /app/app/models/convert_from_ona.rb:30:in `each'
	from /app/app/models/convert_from_ona.rb:30:in `convert'
	from /app/app/models/convert_from_ona.rb:105:in `convert_dataset'
	from /app/bin/convert-from-ona:17:in `import'
	from /app/bin/convert-from-ona:21:in `<main>'

File used in this test case: FPP-Import data.xlsx

Expected:
This field should accept integers as well as strings.
Also, it would be useful if the error was more explicit and informed the user the exact column and cell causing the error.