AssumeRolePolicyDocument TypeError when not using awacs

Using `TemplateGenerator` to import an existing template yields the following error:
```
TypeError: : JustARole.AssumeRolePolicyDocument is , expected (,)
```
The relevant resource:
```
"JustARole":{
"Type":"AWS::IAM::Role",
"Properties":{
"AssumeRolePolicyDocument":{
"Version":"2012-10-17",
"Statement":[{
"Effect":"Allow",
"Principal":{
"Service":["ec2.amazonaws.com"]
},
"Action":["sts:AssumeRole"]
}]
},
"Path":"/"
}
}
```
It seems there's something wrong with fetching the `AssumeRolePolicyDocument` type as it's definitely not a ``.
Installing `troposphere[policy]` made the error disappear. (It appears that the type checking is a bit different when using `awacs`)