Fixing logic for edge case of ap.outputs == nothing

Author: cmhyett

src/systems/unit_check.jl

@@ -214,10 +214,16 @@ function _validate(terms::Vector, labels::Vector{String}; info::String = "")
 end
 
 function _validate(ap::AnalysisPoint; info::String = "")
-    conn_eq = connect(ap.input, ap.outputs...)
-    return _validate(conn_eq.rhs, info=info)
+    is_valid = false
+    if (ap.outputs == nothing)
+        is_valid = true
+    else
+        conn_eq = connect(ap.input, ap.outputs...)
+        is_valid = _validate(conn_eq.rhs, info=info)
+    end
+    return is_valid
 end
-    
+
 function _validate(conn::Connection; info::String = "")
     valid = true
     syss = get_systems(conn)

src/systems/validation.jl

@@ -183,8 +183,14 @@ function _validate(terms::Vector, labels::Vector{String}; info::String = "")
 end
 
 function _validate(ap::AnalysisPoint; info::String = "")
-    conn_eq = connect(ap.input, ap.outputs...)
-    return _validate(conn_eq.rhs, info=info)
+    is_valid = false
+    if (ap.outputs == nothing)
+        is_valid = true
+    else
+        conn_eq = connect(ap.input, ap.outputs...)
+        is_valid = _validate(conn_eq.rhs, info=info)
+    end
+    return is_valid
 end
 
 function _validate(conn::Connection; info::String = "")

test/analysis_points.jl

@@ -53,7 +53,7 @@ using Unitful
         ]
         return System(eqs, t, [], pars; systems, name)
     end
-    @mtkmodel MySquare begin
+    @mtkmodel TestAPAroundUnits begin
         @components begin
             input = UnitfulInput()
         end
@@ -68,8 +68,26 @@ using Unitful
             output ~ input.u^2
         end
     end
-    @named sq = MySquare()
-    @test sq isa System
+    @named sys = TestAPAroundUnits()
+    @test sys isa System
+    
+    @mtkmodel TestAPWithNoOutputs begin
+        @components begin
+            input = UnitfulInput()
+        end
+        @variables begin
+            output(t), [output=true, unit=u"m^2"]
+        end
+        @components begin
+            ub = UnitfulBlock()
+        end
+        @equations begin
+            connect(ub.output, :ap, input)
+            output ~ input.u^2
+        end
+    end
+    @named sys2 = TestAPWithNoOutputs()
+    @test sys2 isa System
 end
 
 @testset "AnalysisPoint is lowered to `connect`" begin