code: public Version getVersion(String rawVersion)
      {
          Version version = this.versions.get(rawVersion);
  
          if (version == null) {
              version = new DefaultVersion(rawVersion);
  
              this.versions.put(rawVersion, version);
          }
  
          return version;
      }
docs: Store and return a weak reference equals to the passed version.
  
  @param rawVersion the version to find
  @return unique instance of {@link VersionConstraint} equals to the passed one