code: function validateBemDeclItem(decl, fileName) {
    let errors = [];
  
    Object.keys(decl).forEach((key) => {
      const val = decl[key];
      if (val === '[object Object]') {
        errors.push(new Error('Error in BemJson ' + fileName +
          ' produced wrong BemDecl ' + JSON.stringify(decl, null, 2)));
      }
    });
  
    return errors;
  }
docs: Validate single BEM declaration
  
  @param {Object} decl
  @param {String} fileName
  @return {Array} of validation errors