Loki: fix missing entries when there arent any derived fields (#78123)

pushing nulls for log entries that does not have a derived field to preserve the order of log data derived fields

public/app/plugins/datasource/loki/getDerivedFields.test.ts

@@ -139,13 +139,13 @@ describe('getDerivedFields', () => {
     });
 
     const trace3 = newFields.find((f) => f.name === 'trace3Name');
-    expect(trace3!.values).toEqual(['bar', 'tar']);
+    expect(trace3!.values).toEqual(['bar', 'tar', null, null]);
     expect(trace3!.config.links![0]).toEqual({
       url: 'http://localhost:8080/${__value.raw}',
       title: '',
     });
 
     const trace4 = newFields.find((f) => f.name === 'trace4Name');
-    expect(trace4!.values).toEqual([]);
+    expect(trace4!.values).toEqual([null, null, null, null]);
   });
 });

public/app/plugins/datasource/loki/getDerivedFields.ts

@@ -40,6 +40,7 @@ export function getDerivedFields(dataFrame: DataFrame, derivedFieldConfigs: Deri
             continue;
           }
         }
+        field.values.push(null);
       } else if (derivedFieldsGrouped[field.name][0].matcherType !== 'regex') {
         // `matcherRegex` will actually be used as a RegExp here
         const line = lineField.values[i];
@@ -50,6 +51,8 @@ export function getDerivedFields(dataFrame: DataFrame, derivedFieldConfigs: Deri
           continue;
         }
 
+        field.values.push(null);
+      } else {
         field.values.push(null);
       }
     }