Fix NoMethodError when RBS file contains class/module alias decl

lib/typeprof/core/ast.rb

@@ -423,7 +423,7 @@ def self.parse_rbs(path, src)
 
       raw_decls.map do |raw_decl|
         AST.create_rbs_decl(raw_decl, lenv)
-      end
+      end.compact
     end
 
     def self.create_rbs_decl(raw_decl, lenv)

scenario/rbs/class-module-alias.rb

@@ -0,0 +1,21 @@
+## update: test.rbs
+class Foo
+  def foo: () -> Integer
+end
+class Bar = Foo
+module M
+  def m: () -> String
+end
+module N = M
+
+## update: test.rb
+def test1
+  Foo.new.foo
+end
+
+## assert: test.rb
+class Object
+  def test1: -> Integer
+end
+
+## diagnostics: test.rb