fix: make "foo#{}" work

Author: mame

lib/typeprof/core/ast/value.rb

@@ -5,7 +5,7 @@ def self.create_part_node(raw_part, lenv)
       when :string_node
         AST.create_node(raw_part, lenv)
       when :embedded_statements_node
-        AST.create_node(raw_part.statements, lenv)
+        raw_part.statements ? AST.create_node(raw_part.statements, lenv) : DummyNilNode.new(TypeProf::CodeRange.from_node(raw_part), lenv)
       when :embedded_variable_node
         AST.create_node(raw_part.variable, lenv)
       else

scenario/misc/dstr.rb

@@ -21,6 +21,16 @@ def bar: (Integer) -> String
   def qux: (Float) -> String
 end
 
+## update
+def foo
+  "foo#{ }"
+end
+
+## assert
+class Object
+  def foo: -> String
+end
+
 ## update
 def xstring_lit(n)
   `echo foo`