Error when joint name start with number

[miquelcampos]

Maya nodes can't start with a number, but depending on the naming rule configuration that can error when joint names are just the index number.
reported in the forum http://forum.mgear-framework.com/t/meta-human-skeleton-errors-w-extra-rig-components-added/2130

# Traceback (most recent call last):
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\guide_manager.py", line 62, in build_from_selection
#     rg.buildFromSelection()
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\__init__.py", line 200, in buildFromSelection
#     self.build()
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\__init__.py", line 226, in build
#     self.processComponents()
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\__init__.py", line 419, in processComponents
#     comp.stepMethods[i]()
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\component\__init__.py", line 158, in step_04
#     self.jointStructure()
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\component\__init__.py", line 1558, in jointStructure
#     gearMulMatrix=gearMulMatrix))
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\component\__init__.py", line 269, in addJoint
#     rot_off=rot_off)
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\shifter\component\__init__.py", line 324, in _addJoint
#     transform.getTransform(obj))
#   File "C:\Users\apfau\Documents\maya\modules\scripts\mgear\core\primitive.py", line 127, in addJoint
#     node.setTransformation(m)
#   File "C:\Program Files\Autodesk\Maya2018\Python\lib\site-packages\pymel\core\general.py", line 1817, in createNode
#     res = cmds.createNode(*args, **kwargs)
#   File "C:\Program Files\Autodesk\Maya2018\Python\lib\site-packages\pymel\internal\pmcmds.py", line 134, in createNode_wrapped
#     res = new_cmd(*new_args, **new_kwargs)
# RuntimeError: New name has no legal characters.