code: public boolean containsValue(Object value) {
          value = maskNull(value);
  
          for (Object val : vals)
              if (value.equals(val))
                  return true;
  
          return false;
      }
docs: Returns <tt>true</tt> if this map maps one or more keys to the
  specified value.
  
  @param value the value whose presence in this map is to be tested
  @return <tt>true</tt> if this map maps one or more keys to this value