[esErrors/isTermSizeZeroError] always return true/false

When the error coming from the elasticsearch.js client is not as expected, isTermSizeZeroError throws a TypeError. This seems incorrect, the function should just return true or false in just about any scenario.

src/ui/public/elasticsearch_errors/__tests__/is_term_size_zero_error.js

@@ -30,4 +30,8 @@ describe('isTermSizeZeroError', () => {
     };
     expect(isTermSizeZeroError(error)).to.be(false);
   });
+
+  it ('returns false for non-elasticsearch error input', () => {
+    expect(isTermSizeZeroError({ foo: 'bar' })).to.be(false);
+  });
 });

src/ui/public/elasticsearch_errors/elasticsearch_error.js

@@ -15,6 +15,17 @@ export default class ElasticsearchError {
     }
   }
 
+  static hasRootCause(error, cause) {
+    try {
+      const esError = new ElasticsearchError(error);
+      return esError.hasRootCause(cause);
+    } catch (err) {
+      // we assume that any failure represents a validation error
+      // in the ElasticsearchError constructor
+      return false;
+    }
+  }
+
   getRootCauses() {
     const rootCauses = _.get(this.error, 'resp.error.root_cause');
     return _.pluck(rootCauses, 'reason');

src/ui/public/elasticsearch_errors/is_term_size_zero_error.js

@@ -1,6 +1,5 @@
-import ElasticsearchError from './elasticsearch_error';
+import { hasRootCause } from './elasticsearch_error';
 
 export default function isTermSizeZeroError(error) {
-  const esError = new ElasticsearchError(error);
-  return esError.hasRootCause('size must be positive, got 0');
+  return hasRootCause(error, 'size must be positive, got 0');
 }