Fix Javadoc view not starting

Null values passed are preserved and sent to HTMLBuilder which sets them
to default colors if needed.
Enhance HTMLBuilder constructor to never allow null colors in it.

Author: akurtakov

bundles/org.eclipse.jface.text/src/org/eclipse/jface/internal/text/html/HTMLPrinter.java

@@ -63,6 +63,11 @@ private static void installColorUpdater(final Display display) {
 	}
 
 	private static org.eclipse.text.html.RGB fromRGB(RGB val) {
+		// Preserve	null RGB as HTMLBuilder contains the default colors and sets them accordingly
+		// in case of null parameter passed
+		if (val == null) {
+			return null;
+		}
 		return new org.eclipse.text.html.RGB(val.red, val.green, val.blue);
 	}
 	private static void cacheColors(Display display) {

bundles/org.eclipse.text/src/org/eclipse/text/html/HTMLBuilder.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2018 IBM Corporation and others.
+ * Copyright (c) 2000, 2024 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -53,10 +53,10 @@ public HTMLBuilder(RGB bg, RGB fg, RGB link, RGB alink) {
 	}
 
 	public void setColors(RGB bg, RGB fg, RGB link, RGB alink) {
-		this.bgColor = bg;
-		this.fgColor = fg;
-		this.linkColor = link;
-		this.alinkColor = alink;
+		this.bgColor = bg != null ? bg : DEFAULT_BG_COLOR_RGB;
+		this.fgColor = fg != null ? fg : DEFAULT_FG_COLOR_RGB;
+		this.linkColor = link != null ? link : DEFAULT_LINK_COLOR_RGB;
+		this.alinkColor = alink != null ? alink : DEFAULT_ACTIVE_LINK_COLOR_RGB;
 	}
 
 	private static String replace(String text, char c, String s) {