Cannot use 'in' operator for 'string'

[strattonn]

<Controllers FormID="d4010c78-1af2-4d44-bcc3-5cb79f3b2dae"> <Controller ID="cbd2b66a-0121-474c-b038-54b9af8bb00e"> <ViewName>Task List</ViewName> <Fields> <Field ID="68fd01c4-a545-91bb-1821-1d90dbec2e69" > </Field> </Fields> </Controller> </Controllers>

Given the preceeding XML, the following will return one node.
xpath.evalFirst(controllerXML, "/Controllers/Controller[@ID='cbd2b66a-0121-474c-b038-54b9af8bb00e']/Fields/Field[@ID='68fd01c4-a545-91bb-1821-1d90dbec2e69']/Name");

The following fails with the message, "Cannot use 'in' operator for 'string'"
xpath.evalFirst(controllerXML, "/Controllers/Controller/Fields/Field[@ID='${fieldId}']/Name");

Line 120 in xpath is the offending line. When it fails json is set to "".
if (node in json) {

Changing line 120 to this fixes the error for me, not sure if that's the best fix.
if (json && node in json) {

[dsummersl]

@strattonn thanks so much for this - I'll write up a test for this and try to get a fix out today.