code: public PropertySourcePropertyResolver addPropertySource(@Nullable PropertySource propertySource) {
          if (propertySource != null) {
              propertySources.put(propertySource.getName(), propertySource);
              processPropertySource(propertySource, propertySource.getConvention());
          }
          return this;
      }
docs: Add a {@link PropertySource} to this resolver.
  
  @param propertySource The {@link PropertySource} to add
  @return This {@link PropertySourcePropertyResolver}