Misc fixes

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);
     }

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) + " ",