help?

[ben-bay]

Running into a bug that doesn't exist when using the Python port of Tracery. When I call grammar.flatten on my rule I get this trace:

.../node_modules/tracery-grammar/tracery.js:657
                    var c = rule.charAt(i);
                                 ^

TypeError: rule.charAt is not a function
    at Object.parse (.../node_modules/tracery-grammar/tracery.js:657:34)
    at TraceryNode.expandChildren (.../node_modules/tracery-grammar/tracery.js:54:36)
    at TraceryNode.expand (.../node_modules/tracery-grammar/tracery.js:94:22)
    at Grammar.expand (.../node_modules/tracery-grammar/tracery.js:512:14)
    at Grammar.flatten (.../node_modules/tracery-grammar/tracery.js:520:25)
    at Object.<anonymous> (.../test_tracery.js:8:29)
    at Module._compile (internal/modules/cjs/loader.js:1139:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1159:10)
    at Module.load (internal/modules/cjs/loader.js:988:32)
    at Function.Module._load (internal/modules/cjs/loader.js:896:14)

What am I doing wrong??