Improved validation error message when env.valueFrom contains no (or misspelled) ref

pkg/api/validation/validation_test.go

@@ -2446,6 +2446,15 @@ func TestValidateEnv(t *testing.T) {
 			}},
 			expectedError: "[0].valueFrom: Invalid value: \"\": may not be specified when `value` is not empty",
 		},
+		{
+			name: "valueFrom without a source",
+			envs: []api.EnvVar{{
+				Name:  "abc",
+				ValueFrom: &api.EnvVarSource{
+				},
+			}},
+			expectedError: "[0].valueFrom: Invalid value: \"\": must specify one of: `fieldRef`, `resourceFieldRef`, `configMapKeyRef` or `secretKeyRef`",
+		},
 		{
 			name: "valueFrom.fieldRef and valueFrom.secretKeyRef specified",
 			envs: []api.EnvVar{{