Fixes none to bool coercion

Fixes #1413 and #1414.

artiq/compiler/transforms/artiq_ir_generator.py

@@ -417,6 +417,8 @@ class ARTIQIRGenerator(algorithm.Visitor):
             length = self.iterable_len(insn)
             return self.append(ir.Compare(ast.NotEq(loc=None), length, ir.Constant(0, length.type)),
                                block=block)
+        elif builtins.is_none(insn.type):
+            return ir.Constant(False, builtins.TBool())
         else:
             note = diagnostic.Diagnostic("note",
                 "this expression has type {type}",