diff --git a/frontend/src/metabase/lib/expressions/formatter.js b/frontend/src/metabase/lib/expressions/formatter.js
index e896b0c82a937e55b965049fd1b860638668d664..0214ce38bd05160025524c15da070da0e58bb5a4 100644
--- a/frontend/src/metabase/lib/expressions/formatter.js
+++ b/frontend/src/metabase/lib/expressions/formatter.js
@@ -15,6 +15,9 @@ export function format(expr, {
     aggregations = VALID_AGGREGATIONS
 }, parens = false) {
     const info = { tableMetadata, customFields, operators, aggregations };
+    if (expr == null) {
+        return "";
+    }
     if (typeof expr === "number") {
         return formatLiteral(expr);
     }
diff --git a/frontend/src/metabase/lib/expressions/parser.js b/frontend/src/metabase/lib/expressions/parser.js
index 399487668cb8ef07afe53e5ff1e58a0660a47308..1b49afef099b4924226a385dd6e9fa20204e488f 100644
--- a/frontend/src/metabase/lib/expressions/parser.js
+++ b/frontend/src/metabase/lib/expressions/parser.js
@@ -287,7 +287,7 @@ export function suggest(source, {
                     prefixTrim: /\w+$/,
                     postfixTrim: /^\w+\s*/
                 })))
-                finalSuggestions.push(...Object.keys(customFields).map(expressionName => ({
+                finalSuggestions.push(...Object.keys(customFields || {}).map(expressionName => ({
                     type: "fields",
                     name: expressionName,
                     text: formatExpressionName(expressionName) + " ",