code: public FaunusPipeline property(final String key, final Class type) {
          this.state.assertNotLocked();
          this.state.assertNoProperty();
          this.state.setProperty(key, type);
          return this;
      }
docs: Emit the property value of an element.
  
  @param key  the key identifying the property
  @param type the class of the property value (so Hadoop can intelligently handle the result)
  @return the extended FaunusPipeline