Robot's get_link_names throws exception for group with one link

[beverlylytle]

Describe the bug Robot's get_link_names throws exception for group with one link

To Reproduce Steps to reproduce the behavior:

1. Load the ur5 demo robot.
2. Run the following code:

try:
    # If testing with the released versions of compas_fab up to 1.0.2, this code will run
    from compas_fab.robots.ur5 import Robot
    robot = Robot()
except:
    # if testing with the main branch (unreleased), this one will do instead
    from compas_fab.robots import RobotLibrary
    robot = RobotLibrary.ur5()

names = robot.get_link_names(group="endeffector")
print(names)

Expected behavior names should equal ['ee_link']

Actual behavior Exception is thrown "Exception: No chain found between the specified element"

[kaniket7209]

Hey @gonzalocasas I want to start my contribution in this good first issue .

[utam-1]

Hi @gonzalocasas, will you assign this issue to me? I have just began learning about open source.

[gonzalocasas]

Hi @gonzalocasas, will you assign this issue to me? I have just began learning about open source.

Done! Thanks!!!

[gonzalocasas]

I will update the example code to the latest version because the one on the description is very old

[gonzalocasas]

I've updated the snippet of code that will cause this bug to make it easier to reproduce. If you have problems while trying to fix this, feel free to post questions here!