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

[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.

With the YAML file described in the issue (#11158), 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[] | 

PR checklist

• Read the contribution guidelines.
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  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

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[wing328]

@ykitamura-mdsol thanks for the fix, which looks good to me.