spring boot @Value Could not resolve placeholder

@Configuration
public class PropertySourcePlaceholderConfig {
    @Bean
    public PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer(){
        PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
        configurer.setIgnoreUnresolvablePlaceholders(true);
        return configurer;
    }
}

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