current in Wire cannot be null (0 instead)

src/main/angular/src/app/editor/junction/Junction.ts

@@ -64,7 +64,6 @@ export class Junction {
     return this.wires
       .filter(wire => wire.traverse(this) !== plus)
       .map(wire => wire.current)
-      .filter(current => current !== null)
       .reduce((a, b) => a + b, 0);
   }
 

src/main/angular/src/app/editor/wire/Wire.ts

@@ -3,7 +3,7 @@ import {RESISTANCE_MIN} from '../circuit/Circuit';
 
 export class Wire {
 
-  current: number | null = null;
+  current: number = 0;
 
   constructor(
     readonly start: Junction,
@@ -18,6 +18,10 @@ export class Wire {
     }
   }
 
+  get absCurrent(): number {
+    return Math.abs(this.current);
+  }
+
   toString() {
     if (this.start.part === this.end.part && this.name !== null) {
       return `'${this.start.part}' "${this.name}"`;