code: function singleToMulti(mapping) {
    const newMapping = {};
    Object.entries(mapping.mapping).forEach(m => {
      newMapping[m[0]] = [m[1]];
    });
    return {
      created: mapping.created,
      fields: [mapping.field],
      key: mapping.key,
      mapping: newMapping
    };
  }
docs: Convert single field mapping to multi field mapping
  @param {object} mapping - single field mapping
  @return {object} multi field mapping