requestContext = (iIndex) => {
			return this.requestContexts(iIndex, 1).then((aResult) => aResult[0]);
		}
Fetches (<code>bAllowRequest</code> must be set to <code>true</code>) or gets the parent node
of a given child node (in case of a recursive hierarchy; see {@link #setAggregation}).

@param {sap.ui.model.odata.v4.Context} oNode
  Some node which could have a parent
@param {boolean} [bAllowRequest]
  Whether it is allowed to send a GET request to fetch the parent node's data
@returns {sap.ui.model.odata.v4.Context|null|undefined|
    Promise<sap.ui.model.odata.v4.Context>|sap.ui.base.SyncPromise}
  <ul>
    <li> The parent node if already known,
    <li> <code>null</code> if the given node is a root node and thus has no parent,
    <li> <code>undefined</code> if the parent node hasn't been read yet and it is not
      allowed to send a request (see <code>bAllowRequest</code>),
    <li> a promise (if a request was sent) which resolves with the parent node or rejects
      with an <code>Error</code> instance.
  </ul>
@throws {Error} If the given node is not part of a recursive hierarchy

@private