result[key]
refers to an object (key), which you initialized as:
key = "project.properties[0]['hudson.model.ParametersDefinitionProperty'] [0].parameterDefinitions[0]['hudson.model.BooleanParameterDefinition']"
In your JSON object, there is no object with that large name, so it doesn't work. If you want to not type out that whole thing, try this:
shortResult = result.project.properties[0]['hudson.model.ParametersDefinitionProperty'][0].parameterDefinitions[0]['hudson.model.BooleanParameterDefinition'];
From here you can access things which are inside "BooleanParameterDefinition".