Add exclude/1 function for Graph builder blocks

.formatter.exs

@@ -3,7 +3,8 @@ locals_without_parens = [
   def_facet_constraint: 2,
   def_applicable_facet: 1,
   bgp: 1,
-  build: 2
+  build: 2,
+  exclude: 1
 ]
 
 [

lib/rdf/graph_builder.ex

@@ -12,6 +12,8 @@ defmodule RDF.Graph.Builder do
     defdelegate a(s, o1, o2, o3), to: RDF.NS.RDF, as: :type
     defdelegate a(s, o1, o2, o3, o4), to: RDF.NS.RDF, as: :type
     defdelegate a(s, o1, o2, o3, o4, o5), to: RDF.NS.RDF, as: :type
+
+    def exclude(_), do: nil
   end
 
   def build({:__block__, _, block}, opts) do

test/unit/graph_builder_test.exs

@@ -490,6 +490,19 @@ defmodule RDF.Graph.BuilderTest do
     end
   end
 
+  test "exclude" do
+    graph =
+      RDF.Graph.build do
+        exclude "this is not a triple"
+
+        EX.S |> EX.p(EX.O)
+
+        exclude "this is not a triple"
+      end
+
+    assert graph == RDF.graph(EX.S |> EX.p(EX.O))
+  end
+
   test "opts" do
     initial = {EX.S, EX.p(), "init"}