Fix Conditional Logic for OmitemptyTag

[abe-tetsu]

Updated the conditional logic to return true when no value is specified for EnableClientJsonOmitemptyTag.

func (c *GenerateConfig) IsEnableClientJsonOmitemptyTag() bool {
	if c == nil {
		return true
	}

	if c.EnableClientJsonOmitemptyTag == nil {
		return true
	}

	return *c.EnableClientJsonOmitemptyTag
}

This ensures that the default behavior remains consistent and returns true when the configuration is not explicitly set.