docs: public TypeDescription.Generic findVariable(String symbol) {
              TypeList.Generic typeVariables = getTypeVariables().filter(named(symbol));
              if (typeVariables.isEmpty()) {
                  TypeVariableSource enclosingSource = getEnclosingSource();
                  return enclosingSource == null
                          ? TypeDescription.Generic.UNDEFINED
                          : enclosingSource.findVariable(symbol);
              } else {
                  return typeVariables.getOnly();
              }
          }