Use explicit value checks where "0" is valid input

User "0", page "0" and edit summary "0" are all valid.
Treating them as empty may cause subtle inconsistencies.

Change-Id: I90a92bfb972cca840e5d8060dac3f116a22990db

includes/api/ApiQueryUserContribs.php

@@ -143,7 +143,9 @@ class ApiQueryUserContribs extends ApiQueryBase {
 						->caller( $fname )
 						->limit( $limit )
 						->whereUserNamePrefix( $this->params['userprefix'] )
-						->where( $fromName ? $dbSecondary->buildComparison( $op, [ 'actor_name' => $fromName ] ) : [] )
+						->where( $fromName !== false
+							? $dbSecondary->buildComparison( $op, [ 'actor_name' => $fromName ] )
+							: [] )
 						->orderByName( $sort )
 						->fetchUserIdentities();
 

includes/block/BlockUtils.php

@@ -143,7 +143,7 @@ class BlockUtils {
 		// This allows validateTarget() to return a "nosuchusershort" message,
 		// which is needed for Special:Block.
 		$canonicalName = $this->userNameUtils->getCanonical( $target );
-		if ( $canonicalName ) {
+		if ( $canonicalName !== false ) {
 			return [
 				new UserIdentityValue( 0, $canonicalName ),
 				AbstractBlock::TYPE_USER

includes/editpage/EditPage.php

@@ -3265,7 +3265,7 @@ class EditPage implements IEditObject {
 			$this->addExplainConflictHeader();
 			$this->editRevId = $this->page->getLatest();
 		} else {
-			if ( $this->section !== '' && $this->section !== 'new' && !$this->summary &&
+			if ( $this->section !== '' && $this->section !== 'new' && $this->summary === '' &&
 				!$this->preview && !$this->diff
 			) {
 				$sectionTitle = self::extractSectionTitle( $this->textbox1 ); // FIXME: use Content object

includes/specials/SpecialContributions.php

@@ -727,16 +727,15 @@ class SpecialContributions extends IncludableSpecialPage {
 			];
 		}
 
-		$target = $this->opts['target'] ?? null;
+		$target = $this->opts['target'] ?? '';
 		$fields['target'] = [
 			'type' => 'user',
-			'default' => $target ?
-				str_replace( '_', ' ', $target ) : '',
+			'default' => str_replace( '_', ' ', $target ),
 			'label' => $this->msg( 'sp-contributions-username' )->text(),
 			'name' => 'target',
 			'id' => 'mw-target-user-or-ip',
 			'size' => 40,
-			'autofocus' => !$target,
+			'autofocus' => $target === '',
 			'section' => 'contribs-top',
 			'ipallowed' => true,
 			'iprange' => true,

includes/specials/SpecialListFiles.php

@@ -88,11 +88,11 @@ class SpecialListFiles extends IncludableSpecialPage {
 		}
 		// Sanitize usernames to avoid symbols in the title of page.
 		$sanitizedUserName = $this->userNameUtils->getCanonical( $userName, UserRigorOptions::RIGOR_NONE );
-		if ( $sanitizedUserName ) {
+		if ( $sanitizedUserName !== false ) {
 			$userName = $sanitizedUserName;
 		}
 
-		if ( $userName ) {
+		if ( $userName !== '' ) {
 			$pageTitle = $this->msg( 'listfiles_subpage' )->plaintextParams( $userName );
 		} else {
 			$pageTitle = $this->msg( 'listfiles' );

includes/specials/SpecialUserRights.php

@@ -710,7 +710,7 @@ class SpecialUserRights extends SpecialPage {
 				'user',
 				'username',
 				30,
-				$this->mTarget ? str_replace( '_', ' ', $this->mTarget ) : '',
+				$this->mTarget !== null ? str_replace( '_', ' ', $this->mTarget ) : '',
 				[
 					'class' => 'mw-autocomplete-user', // used by mediawiki.userSuggest
 				] + (