Skip parsing cause if it is not an Error object

* Merges #2013 from @angrycat9000
    * Fixes #2011

spec/core/ExceptionFormatterSpec.js

@@ -301,6 +301,26 @@ describe('ExceptionFormatter', function() {
           .withContext('first root cause stack frame')
           .toContain('ExceptionFormatterSpec.js');
       });
+
+      it('does not throw if cause is a non Error', function() {
+        const formatter = new jasmineUnderTest.ExceptionFormatter();
+
+        expect(function() {
+          formatter.stack(
+            new Error('error', {
+              cause: function() {}
+            })
+          );
+        }).not.toThrowError();
+
+        expect(function() {
+          formatter.stack(
+            new Error('error', {
+              cause: 'another error'
+            })
+          );
+        }).not.toThrowError();
+      });
     });
   });
 });

src/core/ExceptionFormatter.js

@@ -67,7 +67,7 @@ getJasmineRequireObj().ExceptionFormatter = function(j$) {
         lines.unshift(stackTrace.message);
       }
 
-      if (error.cause) {
+      if (error.cause && error.cause instanceof Error) {
         const substack = this.stack_(error.cause, {
           messageHandling: 'require'
         });