SpringBoot about @ConfigurationPropertie

Why is this method called when create my configure @ConfigurationProperties class

// {@link org.springframework.boot.context.properties.source.ConfigurationPropertyName#convertToOriginalForm}
private CharSequence convertToOriginalForm(CharSequence element) {
    return convertElement(element, false,
    (ch, i) -> ch == '_' || ElementsParser.isValidChar(Character.toLowerCase(ch), i));
}

This operation led to something I didn't expect

# my applciation.yml
config:
  mapping:
    /a: /
    /b: /hello

// my configure class
@Data
@ConfigurationProperties(prefix = "config")
public class Config {

    private final Map<String, String> mapping = new HashMap<>();

}

result: Config->mapping = {"a":"/", "b":"/hello"}

but i expect： Config ->mapping = {"/a":"/", "/b":"/hello"}

Comment From: wilkinsona

This behaviour is described in the documentation. When binding to a map, properties with special characters in their name must by wrapped in [].

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