Bug 1614914 - Fix TypeError in JsPropertyProvider for debugger keyword. r=Honza.

A check is added, as well as a test to ensure everything
is okay.

Differential Revision: https://phabricator.services.mozilla.com/D62599

--HG--
extra : moz-landing-system : lando

devtools/shared/webconsole/js-property-provider.js

@@ -131,6 +131,10 @@ function JSPropertyProvider({
     // Finding the last expression since we've sliced up until the dot.
     // If there were parse errors this won't exist.
     if (lastBody) {
+      if (!lastBody.expression) {
+        return null;
+      }
+
       astExpression = lastBody.expression;
       let matchingObject;
 

devtools/shared/webconsole/test/xpcshell/test_js_property_provider.js

@@ -658,6 +658,10 @@ function runChecks(dbgObject, environment, sandbox) {
 
   results = propertyProvider(`true?<t`);
   test_has_no_results(results);
+
+  // Test autocompletion on debugger statement does not throw
+  results = propertyProvider(`debugger.`);
+  Assert.ok(results === null, "Does not complete a debugger keyword");
 }
 
 /**