code: public Expression get(String name) {
          if (variables.containsKey(name)) {
              return variables.get(name);
          }
          if (parent == null) {
              return new Value("");
          }
          return parent.get(name);
      }
docs: Returns the value previously set for the given variable.
  
  @param name the variable to lookup
  @return the value associated with the given name. Uses the parent scope if no variable with the given
  name exists. Returns a {@link Value} with "" as content, in case the value is completely unknown.