Fix examples for request body with array to not raise java.lang.NullPointerException

Created by: ykitamura-mdsol

Fix example code generators to not raise java.lang.NullPointerException on clients generation for ruby, crystal, go and powershell.

This PR is to close #11158 (closed).

With the YAML file described in the issue (#11158 (closed)), examples will be like these:

Ruby

api_instance = OpenapiClient::PetsApi.new
request_body = [{ ... }] # Array<Object> | 

Go

func main() {
    requestBody := []map[string]interface{}{map[string]interface{}{ ... }} // []map[string]interface{} | 

Powershell

@{ key_example =  ...  } # SystemCollectionsHashtable[] | 

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