The null object does not have a method 'toLowerCase'

[tmst]

When running this script on a discovery document generated by Google cloud tools and published at the appspot.com domain, I get the following error:

NoSuchMethodError: method not found: 'toLowerCase'
Receiver: null
Arguments: []
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 ApisPackageGenerator.generateApiPackage (package:discoveryapis_generator/src/apis_package_generator.dart:70:49)
#2 generateApiPackage (package:discoveryapis_generator/discoveryapis_generator.dart:53:49)
#3 generateAllLibraries (package:discoveryapis_generator/discoveryapis_generator.dart:64:28)
#4 main (file:///home/tom/work/dart/dart-sdk/discoveryapis_generator/bin/generate.dart:112:40)
#5 _startIsolate (dart:isolate-patch/isolate_patch.dart:237)
#6 _startMainIsolate. (dart:isolate-patch/isolate_patch.dart:192)
#7 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:130)

Note: for some reason, my API's discovery document is only 36 lines, considerable shorter than examples I've seen. The discoveryVersion is 'v1'.

[tmst]

I just discovered that there are (at least) two different versions of the discovery document for a given API depending on where it is published - the appspot.com domain or localhost, and that I was probably using the wrong (appspot.com) one.