diff --git a/package-lock.json b/package-lock.json
index 9e923bf..c93bbd1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1149,6 +1149,14 @@
       "resolved": "https://registry.npmjs.org/asn1/-/asn1-0.2.3.tgz",
       "integrity": "sha1-2sh4dxPJlmhJ/IGAd36+nB3fO4Y="
     },
+    "assert": {
+      "version": "1.4.1",
+      "resolved": "https://registry.npmjs.org/assert/-/assert-1.4.1.tgz",
+      "integrity": "sha1-mZEtWRg2tab1s0XA8H7vwI/GXZE=",
+      "requires": {
+        "util": "0.10.3"
+      }
+    },
     "assert-plus": {
       "version": "0.2.0",
       "resolved": "https://registry.npmjs.org/assert-plus/-/assert-plus-0.2.0.tgz",
@@ -3474,11 +3482,13 @@
         },
         "balanced-match": {
           "version": "1.0.0",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
+          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -3491,15 +3501,18 @@
         },
         "code-point-at": {
           "version": "1.1.0",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "concat-map": {
           "version": "0.0.1",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "console-control-strings": {
           "version": "1.1.0",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -3602,7 +3615,8 @@
         },
         "inherits": {
           "version": "2.0.3",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "ini": {
           "version": "1.3.5",
@@ -3612,6 +3626,7 @@
         "is-fullwidth-code-point": {
           "version": "1.0.0",
           "bundled": true,
+          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -3624,17 +3639,20 @@
         "minimatch": {
           "version": "3.0.4",
           "bundled": true,
+          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
         },
         "minimist": {
           "version": "0.0.8",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "minipass": {
           "version": "2.2.4",
           "bundled": true,
+          "optional": true,
           "requires": {
             "safe-buffer": "^5.1.1",
             "yallist": "^3.0.0"
@@ -3651,6 +3669,7 @@
         "mkdirp": {
           "version": "0.5.1",
           "bundled": true,
+          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -3723,7 +3742,8 @@
         },
         "number-is-nan": {
           "version": "1.0.1",
-          "bundled": true
+          "bundled": true,
+          "optional": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -3733,6 +3753,7 @@
         "once": {
           "version": "1.4.0",
           "bundled": true,
+          "optional": true,
           "requires": {
             "wrappy": "1"
           }
@@ -3838,6 +3859,7 @@
         "string-width": {
           "version": "1.0.2",
           "bundled": true,
+          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",
@@ -8120,6 +8142,21 @@
         }
       }
     },
+    "util": {
+      "version": "0.10.3",
+      "resolved": "https://registry.npmjs.org/util/-/util-0.10.3.tgz",
+      "integrity": "sha1-evsa/lCAUkZInj23/g7TeTNqwPk=",
+      "requires": {
+        "inherits": "2.0.1"
+      },
+      "dependencies": {
+        "inherits": {
+          "version": "2.0.1",
+          "resolved": "https://registry.npmjs.org/inherits/-/inherits-2.0.1.tgz",
+          "integrity": "sha1-sX0I0ya0Qj5Wjv9xn5GwscvfafE="
+        }
+      }
+    },
     "util-deprecate": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/util-deprecate/-/util-deprecate-1.0.2.tgz",
diff --git a/package.json b/package.json
index 9ce4bc4..159a9f2 100644
--- a/package.json
+++ b/package.json
@@ -15,6 +15,7 @@
     "lint": "eslint app test"
   },
   "dependencies": {
+    "assert": "^1.4.1",
     "date-range": "0.0.2",
     "js-joda": "^1.8.2",
     "moment": "^2.22.1",