Crash on "no tests no args" input

[vivekhaldar]

On the following input (calc_no_tests_no_args.ss):

given a string containing numbers and operators in reverse polish notation, calculate the result. The expression is given as a list of numbers and operators. Each number may be one of the following: integer, float. You can assume that the expression is always valid.

I get the following backtrace:

python3 parsel.py ./programs/calc_no_tests_no_args.ss  -g -n
python3 parsel.py ./programs/calc_no_tests_no_args.ss  -g -n
Added args: ['rpn_calculator(expression)', 'stack = []', 'for item in expression:', 'if is_number(item):', 'stack.append(item)', 'else:', 'stack.append(apply_operator(item, stack.pop(), stack.pop()))', 'return stack.pop()']
Added args: ['calculate_rpn(expression)', 'stack = []', 'for item in expression:', "if item in '+-*/':", 'b = stack.pop()', 'a = stack.pop()', 'stack.append(eval(a + item + b))', 'else:', 'stack.append(item)', 'return stack[0]']
Added args: ['rpn_calculator(expression)', 'stack = []', 'for item in expression:', 'if is_number(item):', 'stack.append(item)', 'else:', 'stack.append(apply_operator(item, stack.pop(), stack.pop()))', 'return stack.pop()']
Added args: ['rpn(expression)', 'stack = []', 'for item in expression:', "if item in ['+', '-', '*', '/']:", 'a = stack.pop()', 'b = stack.pop()', "if item == '+':", 'stack.append(a + b)', "elif item == '-':", 'stack.append(a - b)', "elif item == '*':", 'stack.append(a * b)', "elif item == '/':", 'stack.append(a / b)', 'else:', 'stack.append(item)', 'return stack.pop()']
Added args: ['rpn_calculator(expression)', 'stack = []', 'for i in expression:', "if i in ['+', '-', '*', '/']:", 'a = stack.pop()', 'b = stack.pop()', "if i == '+':", 'stack.append(a + b)', "elif i == '-':", 'stack.append(b - a)', "elif i == '*':", 'stack.append(a * b)', "elif i == '/':", 'stack.append(b / a)', 'else:', 'stack.append(i)', 'return stack.pop()']
Added args: ['rpn_calculator(expression)', 'stack = []', 'for i in expression:', "if i in ['+', '-', '*', '/']:", 'a = stack.pop()', 'b = stack.pop()', "if i == '+':", 'stack.append(a + b)', "elif i == '-':", 'stack.append(a - b)', "elif i == '*':", 'stack.append(a * b)', "elif i == '/':", 'stack.append(a / b)', 'else:', 'stack.append(i)', 'return stack.pop()']
Added args: ['rpn_calculator(expression)', 'stack = []', 'for element in expression:', "if element in ['+', '-', '*', '/']:", 'a = stack.pop()', 'b = stack.pop()', "if element == '+':", 'stack.append(a + b)', "elif element == '-':", 'stack.append(a - b)', "elif element == '*':", 'stack.append(a * b)', "elif element == '/':", 'stack.append(a / b)', 'else:', 'stack.append(element)', 'return stack.pop()']
Added args: ['rpn_calculator(expression)', 'stack = []', 'for element in expression:', 'if is_number(element):', 'stack.append(element)', 'else:', 'b = stack.pop()', 'a = stack.pop()', 'stack.append(apply_operator(element, a, b))', 'return stack.pop()']
Traceback (most recent call last):
  File "/Users/haldar/parsel/parsel.py", line 650, in <module>
    parsel(codegen, args.source_file, allow_autofill=args.allow_autofill, should_expand=args.allow_expand, debug=debug, add_name_and_args=args.add_name_and_args)
  File "/Users/haldar/parsel/parsel.py", line 617, in parsel
    _, defined_fns = get_graph(program)
  File "/Users/haldar/parsel/graph.py", line 42, in get_graph
    for cur_line in program:
TypeError: 'NoneType' object is not iterable