JsonSerializationException on breaking changes pass

The "Breaking Changes" check for [this PR](https://github.com/Azure/azure-rest-api-specs/pull/4047) is failing with the following somewhat cryptic error:
```
Executing : autorest --input-file=specification/deploymentmanager/resource-manager/Microsoft.DeploymentManager/preview/2018-09-01-preview/deploymentmanager.json --output-artifact=swagger-document.json --output-file=deploymentmanager --output-folder=/tmp/resolved/specification/deploymentmanager/resource-manager/Microsoft.DeploymentManager/preview/2018-09-01-preview
Resolved map for the new specifications:
{ 'specification/deploymentmanager/resource-manager/Microsoft.DeploymentManager/preview/2018-09-01-preview/deploymentmanager.json': '/tmp/resolved/specification/deploymentmanager/resource-manager/Microsoft.DeploymentManager/preview/2018-09-01-preview/deploymentmanager.json' }

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Old Spec: "specification/deploymentmanager/resource-manager/Microsoft.DeploymentManager/preview/2018-09-01-preview/deploymentmanager.json"
New Spec: "/tmp/resolved/specification/deploymentmanager/resource-manager/Microsoft.DeploymentManager/preview/2018-09-01-preview/deploymentmanager.json"
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

{ Error: Command failed: dotnet /home/travis/build/Azure/azure-rest-api-specs/node_modules/oad/lib/dlls/OpenApiDiff.dll -o /tmp/old.json -n /tmp/new.json -JsonValidationMessages

Unhandled Exception: Newtonsoft.Json.JsonSerializationException: Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'AutoRest.Swagger.Model.Operation' because the type requires a JSON object (e.g. {"name":"value"}) to deserialize correctly.
To fix this error either change the JSON to a JSON object (e.g. {"name":"value"}) or change the deserialized type to an array or a type that implements a collection interface (e.g. ICollection, IList) like List that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array.
Path 'paths['/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.DeploymentManager/serviceTopologies/{serviceTopologyName}'].parameters', line 21, position 21.
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureArrayContract(JsonReader reader, Type objectType, JsonContract contract)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateList(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue, String id)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary(IDictionary dictionary, JsonReader reader, JsonDictionaryContract contract, JsonProperty containerProperty, String id)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary(IDictionary dictionary, JsonReader reader, JsonDictionaryContract contract, JsonProperty containerProperty, String id)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
at AutoRest.Swagger.SwaggerModeler.Compare(String swaggerPrevious, String swaggerNew, Settings settings) in /home/travis/build/Azure/openapi-diff/openapi-diff/src/modeler/AutoRest.Swagger/SwaggerModeler.cs:line 18
at OpenApiDiff.Program.Main(String[] args) in /home/travis/build/Azure/openapi-diff/openapi-diff/src/core/OpenApiDiff/Program.cs:line 33
Aborted (core dumped)

at ChildProcess.exithandler (child_process.js:276:12)
at emitTwo (events.js:126:13)
at ChildProcess.emit (events.js:214:7)
at maybeClose (internal/child_process.js:915:16)
at Socket.stream.socket.on (internal/child_process.js:336:11)
at emitOne (events.js:116:13)
at Socket.emit (events.js:211:7)
at Pipe._handle.close [as _onclose] (net.js:561:12)
killed: false,
code: 134,
signal: null,
cmd: 'dotnet /home/travis/build/Azure/azure-rest-api-specs/node_modules/oad/lib/dlls/OpenApiDiff.dll -o /tmp/old.json -n /tmp/new.json -JsonValidationMessages' }
```

There was a breaking change in the PR (one property was renamed) so I would expect it to fail - but that was the only change (apart from descriptions) so I'm not sure what caused this error.

Any thoughts?

Thanks!

Reproduce the failing command against the deploymentmanager specification and inspect the parameters value at the reported path. Start with AutoRest.Swagger/SwaggerModeler.cs line 18 and OpenApiDiff/Program.cs line 33, then verify that the breaking-change check handles the specification and reports the renamed property instead of aborting.

Written by the indexing model from the issue text.