UIRouterGlobals.transition type is incorrectly non-nullable

UIRouterGlobals.transition type is incorrectly non-nullable

Summary

The UIRouterGlobals.transition property is typed as non-nullable (Transition), but at runtime it is null or undefined when there is no active transition (e.g., after a state has fully loaded or on initial page load).

Version

@uirouter/core: 6.1.1

Current Type Definition

export class UIRouterGlobals {
    transition: Transition;
    // ... other properties
}

Expected Type Definition

export class UIRouterGlobals {
    transition: Transition | null | undefined;
    // ... other properties
}

Reproduction

Code Example

import { UIRouterGlobals } from '@uirouter/core';

// In an Angular component during ngOnInit, after the state has loaded:
constructor(private uiRouterGlobals: UIRouterGlobals) {}

ngOnInit(): void {
    // This throws: "can't access property 'to', this.uiRouterGlobals.transition is null"
    const stateName = this.uiRouterGlobals.transition.to().name;
}

Root Cause

When no transition is currently active (which is the normal state after a route has finished loading), uiRouterGlobals.transition is null or undefined. The TypeScript type definition incorrectly claims this property is always present, leading to runtime errors when developers follow the types.

Expected Behavior

The type definition should accurately reflect runtime behavior, allowing TypeScript to catch potential null reference errors at compile time.

Start at the UIRouterGlobals declaration in @uirouter/core and compare the declared transition type with the runtime behavior described in the reproduction. Update the type so it permits the absent-transition cases, then verify that the TypeScript checks cover the nullable usage described by the issue.