fix(select): throwing additional errors if ngModel fails to initialize

If the user has an `md-select` with an `ngModel` that doesn't have a name inside a form, the forms module will throw an error, however Material will also start throwing errors, which may cause confusion. These changes add a null check so our errors don't get mixed up with the forms error.

Fixes #5402.

src/lib/select/select.html

@@ -1,11 +1,11 @@
 <div class="mat-select-trigger" cdk-overlay-origin (click)="toggle()" #origin="cdkOverlayOrigin" #trigger>
   <span
     class="mat-select-placeholder"
-    [class.mat-floating-placeholder]="_selectionModel.hasValue()"
+    [class.mat-floating-placeholder]="_hasValue()"
     [@transformPlaceholder]="_getPlaceholderAnimationState()"
     [style.opacity]="_getPlaceholderOpacity()"
     [style.width.px]="_selectedValueWidth"> {{ placeholder }} </span>
-  <span class="mat-select-value" *ngIf="_selectionModel.hasValue()">
+  <span class="mat-select-value" *ngIf="_hasValue()">
     <span class="mat-select-value-text">{{ triggerValue }}</span>
   </span>
 

src/lib/select/select.spec.ts

@@ -63,7 +63,8 @@ describe('MdSelect', () => {
         BasicSelectWithTheming,
         ResetValuesSelect,
         FalsyValueSelect,
-        SelectWithGroups
+        SelectWithGroups,
+        InvalidSelectInForm
       ],
       providers: [
         {provide: OverlayContainer, useFactory: () => {
@@ -1942,6 +1943,17 @@ describe('MdSelect', () => {
       }).not.toThrow();
     }));
 
+    it('should not throw selection model-related errors in addition to the errors from ngModel',
+      async(() => {
+        const fixture = TestBed.createComponent(InvalidSelectInForm);
+
+        // The first change detection run will throw the "ngModel is missing a name" error.
+        expect(() => fixture.detectChanges()).toThrow();
+
+        // The secound run shouldn't throw selection-model related errors.
+        expect(() => fixture.detectChanges()).not.toThrow();
+      }));
+
   });
 
   describe('change event', () => {
@@ -2842,3 +2854,11 @@ class SelectWithGroups {
   @ViewChild(MdSelect) select: MdSelect;
   @ViewChildren(MdOption) options: QueryList<MdOption>;
 }
+
+
+@Component({
+  template: `<form><md-select [(ngModel)]="value"></md-select></form>`
+})
+class InvalidSelectInForm {
+  value: any;
+}

src/lib/select/select.ts

@@ -547,6 +547,11 @@ export class MdSelect extends _MdSelectMixinBase implements AfterContentInit, On
     this._setScrollTop();
   }
 
+  /** Whether the select has a value. */
+  _hasValue(): boolean {
+    return this._selectionModel && this._selectionModel.hasValue();
+  }
+
   /**
    * Sets the scroll position of the scroll container. This must be called after
    * the overlay pane is attached or the scroll container element will not yet be
@@ -771,7 +776,7 @@ export class MdSelect extends _MdSelectMixinBase implements AfterContentInit, On
     // The farthest the panel can be scrolled before it hits the bottom
     const maxScroll = scrollContainerHeight - panelHeight;
 
-    if (this._selectionModel.hasValue()) {
+    if (this._hasValue()) {
       let selectedOptionOffset = this._getOptionIndex(this._selectionModel.selected[0])!;
 
       selectedOptionOffset += this._getLabelCountBeforeOption(selectedOptionOffset);