config values from yaml file are ignored when docopt has default values

[knoguchi]

Apache Iceberg version

None

Please describe the bug 🐞

Does this really work?
https://github.com/apache/iceberg-go/blob/ba883bdb1d26cc8ea0505e3910ffee0f9c74f315/cmd/iceberg/main.go#L412C1-L428C2

The intention seems to be to copy values from fileConf to resConfig. However, it only copies values when the resConfig fields are empty. Since doctopt sets default values in resConfig, the values read from the file are ignored when a default value already exists.

For example, I set Output: "json" in my config YAML, but this has no effect because resConfig.Output already has a default value of "text".

Is the below better? But which one has precedence when command line args has non-default value, and file config exists for the same option?

func mergeConf(fileConf *config.CatalogConfig, resConfig *Config) {
	if len(fileConf.CatalogType) > 0 {
		resConfig.Catalog = fileConf.CatalogType
	}
	if len(fileConf.URI) > 0 {
		resConfig.URI = fileConf.URI
	}
	if len(fileConf.Output) > 0 {
		resConfig.Output = fileConf.Output
	}
	if len(fileConf.Credential) > 0 {
		resConfig.Cred = fileConf.Credential
	}
	if len(fileConf.Warehouse) > 0 {
		resConfig.Warehouse = fileConf.Warehouse
	}
}