raises IndexError if no laser, rheed sys. or chamber is ever specified

i.e. if one or more of these fields aren't specified thru all layers

src/main.py

@@ -114,8 +114,12 @@ def deduplicate_instruments_from_layers(layers):
         ded_chambers = list( set( chambers ) )
         ded_rheeds = list( set( rheeds ) )
         elegant_list = [ ded_lasers, ded_chambers, ded_rheeds]
+    if 0 in [ len(i) for i in elegant_list ]:
+        # i.e. if length of one of the lists in elegant_list is zero (missing data):
+        raise IndexError("Missing data: no Laser System, Chamber and/or RHEED System is specified in any of the Deposition-type experiments related to this sample.")
     if not all([ len(i) == 1 for i in elegant_list ]):
         print("Warning: different instruments have been used for different layers - which is currently not allowed.")
+        # for every element in elegant list check if len > 1 and if it is 
         print("Selecting the first occurence for every category...")
     instruments_used_dict = {
         "laser_system": ded_lasers[0],