add test, fix bugs

src/instruct.jl

@@ -18,6 +18,15 @@ const SPECIALIZATION_LIST = Symbol[:X, :Y, :Z, :S, :T, :Sdag, :Tdag]
 const Locations{T} = NTuple{N, T} where N
 const BitConfigs{T} = NTuple{N, T} where N
 
+function YaoBase.instruct!(
+    state::AbstractVecOrMat{T1},
+    operator::AbstractMatrix{T2},
+    locs::Tuple{},
+    control_locs::NTuple{C, Int}=(),
+    control_bits::NTuple{C, Int}=()) where {T1, T2, M, C}
+    return state
+end
+
 function YaoBase.instruct!(
     state::AbstractVecOrMat{T1},
     operator::AbstractMatrix{T2},
@@ -44,6 +53,15 @@ function YaoBase.instruct!(state::AbstractVecOrMat{T1}, U1::SDDiagonal{T2}, loc:
     return instruct!(state, copyto!(similar(U1, T1), U1), loc)
 end
 
+function YaoBase.instruct!(
+    state::AbstractVecOrMat{T},
+    operator::AbstractMatrix{T},
+    locs::Tuple{},
+    control_locs::NTuple{C, Int} = (),
+    control_bits::NTuple{C, Int} = ()) where {T, M, C}
+    return state
+end
+
 function YaoBase.instruct!(
     state::AbstractVecOrMat{T},
     operator::AbstractMatrix{T},
@@ -193,7 +211,7 @@ for (G, FACTOR) in zip([:Z, :S, :T, :Sdag, :Tdag], [:(-1), :(im), :($(exp(im*π/
         instruct!(state, g, locs...)
 
     # no effect (to fix ambiguity)
-    @eval YaoBase.instruct!(::AbstractVecOrMat, ::Val{$(QuoteNode(G))}, ::Tuple{}) = nothing
+    @eval YaoBase.instruct!(st::AbstractVecOrMat, ::Val{$(QuoteNode(G))}, ::Tuple{}) = st
 
     @eval function YaoBase.instruct!(state::AbstractVecOrMat{T}, ::Val{$(QuoteNode(G))}, locs::Int) where T
         mask = bmask(locs)

test/instruct.jl

@@ -95,3 +95,13 @@ end
     st = rand(1<<4)
     @test instruct!(st, IMatrix{2, Float64}(), 1) == st
 end
+
+@testset "test empty locs" begin
+    st = rand(ComplexF64, 1<<4)
+    pm = pmrand(ComplexF64, 2)
+    @test instruct!(copy(st), pm, ()) == st
+
+    for G in [:Z, :S, :T, :Sdag, :Tdag]
+        @test instruct!(copy(st), Val(G), ()) == st
+    end
+end