Support patching values out of the configuration.

A configuration patch having keys with null values will result
in those keys being removed from the configuration.

lib/www/server/lib/db/project/configuration/patch.js

@@ -1,5 +1,5 @@
 const { setSurvey } = require('../../connection');
-const { deepMerge } = require('../../../utils');
+const { deepMerge, removeNulls } = require('../../../utils');
 const { modify } = require('../create');
 
 
@@ -36,7 +36,7 @@ async function patch (projectId, payload, opts = {}) {
 			}
 		}
 
-		const dest = deepMerge(source, payload);
+		const dest = removeNulls(deepMerge(source, payload));
 		await modify(projectId, dest);
 		return dest;
 

lib/www/server/lib/utils/index.js

@@ -4,5 +4,6 @@ module.exports = {
 	dms: require('./dms'),
 	replaceMarkers: require('./replaceMarkers'),
 	flattenQCDefinitions: require('./flattenQCDefinitions'),
-	deepMerge: require('./deepMerge')
+	deepMerge: require('./deepMerge'),
+	removeNulls: require('./removeNulls')
 };

lib/www/server/lib/utils/removeNulls.js

@@ -0,0 +1,23 @@
+
+/**
+ * Delete keys whose value is null.
+ *
+ */
+function removeNulls (obj) {
+
+	function getType (obj) {
+		return Object.prototype.toString.call(obj).slice(8, -1).toLowerCase();
+	}
+
+	for (let [key, value] of Object.entries(obj)) {
+		if (value === null) {
+			delete obj[key];
+		} else if (getType(value) == "object") {
+			removeNulls(value);
+		}
+	}
+
+	return obj;
+}
+
+module.exports = removeNulls;