It appears that the repository has undergone several changes and renamings:

backend/node_modules/postcss-value-parser/lib/index.js

@@ -1,28 +0,0 @@
-var parse = require("./parse");
-var walk = require("./walk");
-var stringify = require("./stringify");
-
-function ValueParser(value) {
-  if (this instanceof ValueParser) {
-    this.nodes = parse(value);
-    return this;
-  }
-  return new ValueParser(value);
-}
-
-ValueParser.prototype.toString = function() {
-  return Array.isArray(this.nodes) ? stringify(this.nodes) : "";
-};
-
-ValueParser.prototype.walk = function(cb, bubble) {
-  walk(this.nodes, cb, bubble);
-  return this;
-};
-
-ValueParser.unit = require("./unit");
-
-ValueParser.walk = walk;
-
-ValueParser.stringify = stringify;
-
-module.exports = ValueParser;