Handle empty case in other function

Author: JoeyT1994

src/abstractitensornetwork.jl

@@ -629,7 +629,7 @@ end
 
 #Get the path that moves the gauge from a to b on a tree
 #TODO: Move to NamedGraphs
-function gauge_path(g::AbstractGraph, region_a::Vector, region_b::Vector)
+function edge_sequence_between_regions(g::AbstractGraph, region_a::Vector, region_b::Vector)
   issetequal(region_a, region_b) && return edgetype(g)[]
   st = steiner_tree(g, union(region_a, region_b))
   path = post_order_dfs_edges(st, first(region_b))
@@ -646,10 +646,8 @@ function tree_gauge(
   new_region::Vector;
   kwargs...,
 )
-  path = gauge_path(ψ, cur_region, new_region)
-  if !isempty(path)
-    ψ = gauge_walk(alg, ψ, path; kwargs...)
-  end
+  es = edge_sequence_between_regions(ψ, cur_region, new_region)
+  ψ = gauge_walk(alg, ψ, es; kwargs...)
   return ψ
 end