Correctly deal with non-array rule specifications

index.js

@@ -2,6 +2,7 @@
 
 const asExpression = require("as-expression");
 const defaultValue = require("default-value");
+const assureArray = require("assure-array");
 const flatten = require("flatten");
 
 const ValidationError = require("@validatem/error");
@@ -15,7 +16,7 @@ function containsRules(rules) {
 		return false;
 	} else {
 		// TODO: Switch to `Array#flat` once Node 10.x goes EOL (April 2021)
-		let flattenedRules = flatten(rules);
+		let flattenedRules = flatten(assureArray(rules));
 
 		if (!flattenedRules.some((rule) => rule != null)) {
 			return false;

package.json

@@ -17,6 +17,7 @@
     "@validatem/error": "^1.0.0",
     "@validatem/validation-result": "^0.1.1",
     "as-expression": "^1.0.0",
+    "assure-array": "^1.0.0",
     "default-value": "^1.0.0",
     "flatten": "^1.0.3"
   },