codegen errors for query case without parameters

related https://github.com/CosmWasm/cosmwasm/issues/1416

example https://github.com/grod220/ts-codegen-example

schema https://gist.github.com/pyramation/97af26385c9348688c74e849898ce419

the generated code that causes an issue (the enum):

```json
"execute": {
"$schema": "http://json-schema.org/draft-07/schema#",
"title": "ExecuteMsg",
"oneOf": [
{
"type": "string",
"enum": [
"accept_ownership"
]
},
{
"description": "Due to some chains being permissioned via governance, we must instantiate this contract first and give ownership access to Rover contract with this action after both are independently deployed.",
"type": "object",
"required": [
"propose_new_owner"
],
"properties": {
"propose_new_owner": {
"type": "object",
"required": [
"new_owner"
],
"properties": {
"new_owner": {
"type": "string"
}
}
}
},
"additionalProperties": false
},
...
```

Start by reviewing the related CosmWasm issue, the ts-codegen-example repository, and the linked schema, then reproduce generation for the shown ExecuteMsg enum. Trace the generated code for the no-parameter query case and confirm that code generation completes without the reported error.

索引モデルが issue の本文から書いたものです。