code: function getOptTypesFrom(block, name) {
    var types = getTypesFrom_(block, name);
    if (types.length == 0) {
      return undefined;
    } else if (types.indexOf('null') != -1) {
      return 'null';
    } else if (types.length == 1) {
      return types[0];
    } else {
      return '[' + types.join(', ') + ']';
    }
  }
docs: Fetch the type(s) defined in the given input.
  Format as a string for appending to the generated code.
  @param {!Blockly.Block} block Block with input.
  @param {string} name Name of the input.
  @return {?string} String defining the types.