NPE in SecureASTCustomizer for interface method declarations

        final SecuringCodeVisitor visitor = new SecuringCodeVisitor();
        ast.getStatementBlock().visit(visitor);
        for (ClassNode clNode : ast.getClasses()) {
            if (clNode!=classNode) {
                checkMethodDefinitionAllowed(clNode);
                for (MethodNode methodNode : clNode.getMethods()) {
                    if (!methodNode.isSynthetic()) {
=>                      methodNode.getCode().visit(visitor);
                    }
                }
            }
        }