function getValidDeps(node) {
  if (!node || node.type !== 'ArrayExpression' || !node.elements) {
    return;
  }

  var deps = [];

  node.elements.some(function(elem) {
    if (elem.type === 'Literal') {
      deps.push(elem.value);
    }
  });

  return deps.length ? deps : undefined;
}
Pulls out dependencies from an array literal with just string members.
If string literals, will just return those string values in an array,
skipping other items in the array.

@param {Node} node an AST node.

@returns {Array} an array of strings.
If null is returned, then it means the input node was not a valid
dependency.