Bug 125420 [Commands] parameters: allow commands to specify return type
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
*            The id of the parameter to retrieve.
	 * @return The parameter with the provided id or <code>null</code> if this
	 *         command does not have a parameter with the id.
	 * @throws NotDefinedException
	 *             If the handle is not currently defined.
	 * @since 3.2
	 */
	public final IParameter getParameter(final String parameterId)
			throws NotDefinedException {
		if (!isDefined()) {
			throw new NotDefinedException(
					"Cannot get a parameter from an undefined command"); 
		}
		if (parameters == null) {
			return null;
		}
		for (int i = 0; i < parameters.length; i++) {
			final IParameter parameter = parameters[i];
			if (parameter.getId().equals(parameterId)) {
				return parameter;
			}
		}
		return null;
	}
	/**
	 * Returns the parameters for this command. This call triggers provides a
	 * copy of the array, so excessive calls to this method should be avoided.
	 * 
	 * @return The parameters for this command. This value might be
	 *         <code>null</code>, if the command has no parameters.