Apply layers on blank lines

Layers were not being applied because there was no gr-text element
rendered for blank lines. To apply layers, we need lineElement,
textElement, and GrDiffLine element to be present.

Rendering this action may result in the creation of additional HTML nodes.

Change-Id: Id6b3ef8b7fec0fdbc65e14c68aa8b602eebdef82
Release-Notes: skip
Google-Bug-Id: b/345126277

polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
index 642610a..1caaebd 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
@@ -573,11 +573,11 @@
     // Note that `this.layersApplied` will wipe away the <gr-diff-text>, and
     // another rendering cycle will be initiated in `updated()`.
     // prettier-ignore
-    const textElement = line?.text && !this.layersApplied
+    const textElement = !this.layersApplied
       ? html`<gr-diff-text
           ${ref(this.contentRef(side))}
           data-side=${ifDefined(side)}
-          .text=${line?.text}
+          .text=${line?.text ?? ''}
           .tabSize=${this.tabSize}
           .lineLimit=${this.lineLength}
           .isResponsive=${isResponsive(this.responsiveMode)}

polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts
index 1526ce3..346d3fe 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts
@@ -164,7 +164,9 @@
             >
               <td class="blankLineNum left"></td>
               <td class="blank left no-intraline-info">
-                <div class="contentText" data-side="left"></div>
+                <div class="contentText" data-side="left">
+                  <gr-diff-text data-side="left"></gr-diff-text>
+                </div>
               </td>
               <td class="lineNum right" data-value="1">
                 <button
@@ -226,7 +228,9 @@
               </td>
               <td class="blankLineNum right"></td>
               <td class="blank no-intraline-info right">
-                <div class="contentText" data-side="right"></div>
+                <div class="contentText" data-side="right">
+                  <gr-diff-text data-side="right"></gr-diff-text>
+                </div>
               </td>
             </tr>
             <slot name="post-left-line-1"></slot>