diff --git a/cypress/helpers/util.ts b/cypress/helpers/util.ts
index 9e49d965e..3ffba697a 100644
--- a/cypress/helpers/util.ts
+++ b/cypress/helpers/util.ts
@@ -54,11 +54,11 @@ export const imgSnapshotTest = (
 ): void => {
   const options: CypressMermaidConfig = {
     ..._options,
-    fontFamily: _options.fontFamily || 'courier',
+    fontFamily: _options.fontFamily ?? 'courier',
     // @ts-ignore TODO: Fix type of fontSize
-    fontSize: _options.fontSize || '16px',
+    fontSize: _options.fontSize ?? '16px',
     sequence: {
-      ...(_options.sequence || {}),
+      ...(_options.sequence ?? {}),
       actorFontFamily: 'courier',
       noteFontFamily: _options.sequence?.noteFontFamily
         ? _options.sequence.noteFontFamily
@@ -94,7 +94,7 @@ export const openURLAndVerifyRendering = (
   options: CypressMermaidConfig,
   validation?: any
 ): void => {
-  const name: string = (options.name || cy.state('runnable').fullTitle()).replace(/\s+/g, '-');
+  const name: string = (options.name ?? cy.state('runnable').fullTitle()).replace(/\s+/g, '-');
 
   cy.visit(url);
   cy.window().should('have.property', 'rendered', true);
diff --git a/eslint.config.js b/eslint.config.js
index 8b4807bc5..ed703ea71 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -109,7 +109,6 @@ export default tseslint.config(
       '@typescript-eslint/no-unsafe-member-access': 'off',
       '@typescript-eslint/no-unsafe-return': 'off',
       '@typescript-eslint/only-throw-error': 'warn',
-      '@typescript-eslint/prefer-nullish-coalescing': 'warn',
       '@typescript-eslint/prefer-promise-reject-errors': 'warn',
       // END
       'json/*': ['error', 'allowComments'],
diff --git a/packages/mermaid/scripts/docs.mts b/packages/mermaid/scripts/docs.mts
index 06cea376d..374e78870 100644
--- a/packages/mermaid/scripts/docs.mts
+++ b/packages/mermaid/scripts/docs.mts
@@ -181,10 +181,10 @@ export const transformToBlockQuote = (
 ) => {
   if (vitepress) {
     const vitepressType = type === 'note' ? 'info' : type;
-    return `::: ${vitepressType} ${customTitle || ''}\n${content}\n:::`;
+    return `::: ${vitepressType} ${customTitle ?? ''}\n${content}\n:::`;
   } else {
-    const icon = blockIcons[type] || '';
-    const title = `${icon}${customTitle || capitalize(type)}`;
+    const icon = blockIcons[type] ?? '';
+    const title = `${icon}${customTitle ?? capitalize(type)}`;
     return `> **${title}** \n> ${content.replace(/\n/g, '\n> ')}`;
   }
 };
diff --git a/packages/mermaid/src/diagrams/block/blockDB.ts b/packages/mermaid/src/diagrams/block/blockDB.ts
index edd8a9c50..d6e35ed15 100644
--- a/packages/mermaid/src/diagrams/block/blockDB.ts
+++ b/packages/mermaid/src/diagrams/block/blockDB.ts
@@ -101,7 +101,7 @@ const populateBlockDatabase = (_blockList: Block[], parent: Block): void => {
       continue;
     }
     if (block.type === 'applyClass') {
-      setCssClass(block.id, block?.styleClass || '');
+      setCssClass(block.id, block?.styleClass ?? '');
       continue;
     }
     if (block.type === 'applyStyles') {
@@ -111,7 +111,7 @@ const populateBlockDatabase = (_blockList: Block[], parent: Block): void => {
       continue;
     }
     if (block.type === 'column-setting') {
-      parent.columns = block.columns || -1;
+      parent.columns = block.columns ?? -1;
     } else if (block.type === 'edge') {
       const count = (edgeCount.get(block.id) ?? 0) + 1;
       edgeCount.set(block.id, count);
@@ -145,7 +145,7 @@ const populateBlockDatabase = (_blockList: Block[], parent: Block): void => {
       }
       if (block.type === 'space') {
         // log.debug('abc95 space', block);
-        const w = block.width || 1;
+        const w = block.width ?? 1;
         for (let j = 0; j < w; j++) {
           const newBlock = clone(block);
           newBlock.id = newBlock.id + '-' + j;
diff --git a/packages/mermaid/src/diagrams/block/layout.ts b/packages/mermaid/src/diagrams/block/layout.ts
index 4dfd0b0d6..7f44a5f19 100644
--- a/packages/mermaid/src/diagrams/block/layout.ts
+++ b/packages/mermaid/src/diagrams/block/layout.ts
@@ -2,7 +2,8 @@ import type { BlockDB } from './blockDB.js';
 import type { Block } from './blockTypes.js';
 import { log } from '../../logger.js';
 import { getConfig } from '../../diagram-api/diagramAPI.js';
-const padding = getConfig()?.block?.padding || 8;
+// TODO: This means the number we provide in diagram's config will never be used. Should fix.
+const padding = getConfig()?.block?.padding ?? 8;
 
 interface BlockPosition {
   px: number;
@@ -42,7 +43,7 @@ const getMaxChildSize = (block: Block) => {
   // find max width of children
   // log.debug('getMaxChildSize abc95 (start) parent:', block.id);
   for (const child of block.children) {
-    const { width, height, x, y } = child.size || { width: 0, height: 0, x: 0, y: 0 };
+    const { width, height, x, y } = child.size ?? { width: 0, height: 0, x: 0, y: 0 };
     log.debug(
       'getMaxChildSize abc95 child:',
       child.id,
@@ -60,7 +61,7 @@ const getMaxChildSize = (block: Block) => {
       continue;
     }
     if (width > maxWidth) {
-      maxWidth = width / (block.widthInColumns || 1);
+      maxWidth = width / (block.widthInColumns ?? 1);
     }
     if (height > maxHeight) {
       maxHeight = height;
@@ -107,7 +108,7 @@ function setBlockSizes(block: Block, db: BlockDB, siblingWidth = 0, siblingHeigh
           `abc95 Setting size of children of ${block.id} id=${child.id} ${maxWidth} ${maxHeight} ${JSON.stringify(child.size)}`
         );
         child.size.width =
-          maxWidth * (child.widthInColumns || 1) + padding * ((child.widthInColumns || 1) - 1);
+          maxWidth * (child.widthInColumns ?? 1) + padding * ((child.widthInColumns ?? 1) - 1);
         child.size.height = maxHeight;
         child.size.x = 0;
         child.size.y = 0;
@@ -121,10 +122,10 @@ function setBlockSizes(block: Block, db: BlockDB, siblingWidth = 0, siblingHeigh
       setBlockSizes(child, db, maxWidth, maxHeight);
     }
 
-    const columns = block.columns || -1;
+    const columns = block.columns ?? -1;
     let numItems = 0;
     for (const child of block.children) {
-      numItems += child.widthInColumns || 1;
+      numItems += child.widthInColumns ?? 1;
     }
 
     // The width and height in number blocks
@@ -204,13 +205,13 @@ function layoutBlocks(block: Block, db: BlockDB) {
   log.debug(
     `abc85 layout blocks (=>layoutBlocks) ${block.id} x: ${block?.size?.x} y: ${block?.size?.y} width: ${block?.size?.width}`
   );
-  const columns = block.columns || -1;
+  const columns = block.columns ?? -1;
   log.debug('layoutBlocks columns abc95', block.id, '=>', columns, block);
   if (
     block.children && // find max width of children
     block.children.length > 0
   ) {
-    const width = block?.children[0]?.size?.width || 0;
+    const width = block?.children[0]?.size?.width ?? 0;
     const widthOfChildren = block.children.length * width + (block.children.length - 1) * padding;
 
     log.debug('widthOfChildren 88', widthOfChildren, 'posX');
@@ -249,7 +250,7 @@ function layoutBlocks(block: Block, db: BlockDB) {
           } ${halfWidth} padding=${padding} width=${width} halfWidth=${halfWidth} => x:${
             child.size.x
           } y:${child.size.y} ${child.widthInColumns} (width * (child?.w || 1)) / 2 ${
-            (width * (child?.widthInColumns || 1)) / 2
+            (width * (child?.widthInColumns ?? 1)) / 2
           }`
         );
 
@@ -263,15 +264,13 @@ function layoutBlocks(block: Block, db: BlockDB) {
             child.id
           }startingPosX${startingPosX}${padding}${halfWidth}=>x:${child.size.x}y:${child.size.y}${
             child.widthInColumns
-          }(width * (child?.w || 1)) / 2${(width * (child?.widthInColumns || 1)) / 2}`
+          }(width * (child?.w || 1)) / 2${(width * (child?.widthInColumns ?? 1)) / 2}`
         );
       }
-
-      // posY += height + padding;
       if (child.children) {
         layoutBlocks(child, db);
       }
-      columnPos += child?.widthInColumns || 1;
+      columnPos += child?.widthInColumns ?? 1;
       log.debug('abc88 columnsPos', child, columnPos);
     }
   }
diff --git a/packages/mermaid/src/diagrams/block/renderHelpers.ts b/packages/mermaid/src/diagrams/block/renderHelpers.ts
index 9dffafd76..97eca4074 100644
--- a/packages/mermaid/src/diagrams/block/renderHelpers.ts
+++ b/packages/mermaid/src/diagrams/block/renderHelpers.ts
@@ -11,7 +11,7 @@ function getNodeFromBlock(block: Block, db: BlockDB, positioned = false) {
 
   let classStr = 'default';
   if ((vertex?.classes?.length || 0) > 0) {
-    classStr = (vertex?.classes || []).join(' ');
+    classStr = (vertex?.classes ?? []).join(' ');
   }
   classStr = classStr + ' flowchart-label';
 
@@ -85,12 +85,12 @@ function getNodeFromBlock(block: Block, db: BlockDB, positioned = false) {
       shape = 'rect';
   }
 
-  const styles = getStylesFromArray(vertex?.styles || []);
+  const styles = getStylesFromArray(vertex?.styles ?? []);
 
   // Use vertex id as text in the box if no text is provided by the graph definition
   const vertexText = vertex.label;
 
-  const bounds = vertex.size || { width: 0, height: 0, x: 0, y: 0 };
+  const bounds = vertex.size ?? { width: 0, height: 0, x: 0, y: 0 };
   // Add the node
   const node = {
     labelStyle: styles.labelStyle,
@@ -109,7 +109,7 @@ function getNodeFromBlock(block: Block, db: BlockDB, positioned = false) {
     positioned,
     intersect: undefined,
     type: vertex.type,
-    padding: padding ?? (getConfig()?.block?.padding || 0),
+    padding: padding ?? getConfig()?.block?.padding ?? 0,
   };
   return node;
 }
diff --git a/packages/mermaid/src/diagrams/common/common.ts b/packages/mermaid/src/diagrams/common/common.ts
index c3e36d087..e24c8e85c 100644
--- a/packages/mermaid/src/diagrams/common/common.ts
+++ b/packages/mermaid/src/diagrams/common/common.ts
@@ -34,13 +34,13 @@ function setupDompurifyHooks() {
 
   DOMPurify.addHook('beforeSanitizeAttributes', (node: Element) => {
     if (node.tagName === 'A' && node.hasAttribute('target')) {
-      node.setAttribute(TEMPORARY_ATTRIBUTE, node.getAttribute('target') || '');
+      node.setAttribute(TEMPORARY_ATTRIBUTE, node.getAttribute('target') ?? '');
     }
   });
 
   DOMPurify.addHook('afterSanitizeAttributes', (node: Element) => {
     if (node.tagName === 'A' && node.hasAttribute(TEMPORARY_ATTRIBUTE)) {
-      node.setAttribute('target', node.getAttribute(TEMPORARY_ATTRIBUTE) || '');
+      node.setAttribute('target', node.getAttribute(TEMPORARY_ATTRIBUTE) ?? '');
       node.removeAttribute(TEMPORARY_ATTRIBUTE);
       if (node.getAttribute('target') === '_blank') {
         node.setAttribute('rel', 'noopener');
diff --git a/packages/mermaid/src/diagrams/flowchart/flowDb.ts b/packages/mermaid/src/diagrams/flowchart/flowDb.ts
index 985f5db46..d03f1d989 100644
--- a/packages/mermaid/src/diagrams/flowchart/flowDb.ts
+++ b/packages/mermaid/src/diagrams/flowchart/flowDb.ts
@@ -503,7 +503,7 @@ export const addSubGraph = function (
     }
   }
 
-  id = id || 'subGraph' + subCount;
+  id = id ?? 'subGraph' + subCount;
   title = title || '';
   title = sanitizeText(title);
   subCount = subCount + 1;
diff --git a/packages/mermaid/src/diagrams/flowchart/flowRenderer-v2.js b/packages/mermaid/src/diagrams/flowchart/flowRenderer-v2.js
index d291f31d6..1dce1391e 100644
--- a/packages/mermaid/src/diagrams/flowchart/flowRenderer-v2.js
+++ b/packages/mermaid/src/diagrams/flowchart/flowRenderer-v2.js
@@ -366,8 +366,8 @@ export const draw = async function (text, id, _version, diagObj) {
   }
 
   const { securityLevel, flowchart: conf } = getConfig();
-  const nodeSpacing = conf.nodeSpacing || 50;
-  const rankSpacing = conf.rankSpacing || 50;
+  const nodeSpacing = conf.nodeSpacing ?? 50;
+  const rankSpacing = conf.rankSpacing ?? 50;
 
   // Handle root and document for when rendering in sandbox mode
   let sandboxElement;
diff --git a/packages/mermaid/src/diagrams/flowchart/flowRenderer.js b/packages/mermaid/src/diagrams/flowchart/flowRenderer.js
index 8b261e66c..314c6aa52 100644
--- a/packages/mermaid/src/diagrams/flowchart/flowRenderer.js
+++ b/packages/mermaid/src/diagrams/flowchart/flowRenderer.js
@@ -301,8 +301,8 @@ export const draw = async function (text, id, _version, diagObj) {
   if (dir === undefined) {
     dir = 'TD';
   }
-  const nodeSpacing = conf.nodeSpacing || 50;
-  const rankSpacing = conf.rankSpacing || 50;
+  const nodeSpacing = conf.nodeSpacing ?? 50;
+  const rankSpacing = conf.rankSpacing ?? 50;
 
   // Create the input mermaid.graph
   const g = new graphlib.Graph({
diff --git a/packages/mermaid/src/diagrams/quadrant-chart/quadrantBuilder.ts b/packages/mermaid/src/diagrams/quadrant-chart/quadrantBuilder.ts
index 567465c78..c7d478ed1 100644
--- a/packages/mermaid/src/diagrams/quadrant-chart/quadrantBuilder.ts
+++ b/packages/mermaid/src/diagrams/quadrant-chart/quadrantBuilder.ts
@@ -493,8 +493,8 @@ export class QuadrantBuilder {
       const props: QuadrantPointType = {
         x: xAxis(point.x),
         y: yAxis(point.y),
-        fill: point.color || this.themeConfig.quadrantPointFill,
-        radius: point.radius || this.config.pointRadius,
+        fill: point.color ?? this.themeConfig.quadrantPointFill,
+        radius: point.radius ?? this.config.pointRadius,
         text: {
           text: point.text,
           fill: this.themeConfig.quadrantPointTextFill,
@@ -505,8 +505,8 @@ export class QuadrantBuilder {
           fontSize: this.config.pointLabelFontSize,
           rotation: 0,
         },
-        strokeColor: point.strokeColor || this.themeConfig.quadrantPointFill,
-        strokeWidth: point.strokeWidth || '0px',
+        strokeColor: point.strokeColor ?? this.themeConfig.quadrantPointFill,
+        strokeWidth: point.strokeWidth ?? '0px',
       };
       return props;
     });
diff --git a/packages/mermaid/src/diagrams/quadrant-chart/quadrantRenderer.ts b/packages/mermaid/src/diagrams/quadrant-chart/quadrantRenderer.ts
index c2295da4d..6d2435cd4 100644
--- a/packages/mermaid/src/diagrams/quadrant-chart/quadrantRenderer.ts
+++ b/packages/mermaid/src/diagrams/quadrant-chart/quadrantRenderer.ts
@@ -46,10 +46,10 @@ export const draw = (txt: string, id: string, _version: string, diagObj: Diagram
 
   const group = svg.append('g').attr('class', 'main');
 
-  const width = conf.quadrantChart?.chartWidth || 500;
-  const height = conf.quadrantChart?.chartHeight || 500;
+  const width = conf.quadrantChart?.chartWidth ?? 500;
+  const height = conf.quadrantChart?.chartHeight ?? 500;
 
-  configureSvgSize(svg, height, width, conf.quadrantChart?.useMaxWidth || true);
+  configureSvgSize(svg, height, width, conf.quadrantChart?.useMaxWidth ?? true);
 
   svg.attr('viewBox', '0 0 ' + width + ' ' + height);
 
diff --git a/packages/mermaid/src/diagrams/sankey/sankeyRenderer.ts b/packages/mermaid/src/diagrams/sankey/sankeyRenderer.ts
index c72eaf7b6..a981a346e 100644
--- a/packages/mermaid/src/diagrams/sankey/sankeyRenderer.ts
+++ b/packages/mermaid/src/diagrams/sankey/sankeyRenderer.ts
@@ -5,7 +5,6 @@ import {
   scaleOrdinal as d3scaleOrdinal,
   schemeTableau10 as d3schemeTableau10,
 } from 'd3';
-
 import type { SankeyNode as d3SankeyNode } from 'd3-sankey';
 import {
   sankey as d3Sankey,
@@ -160,7 +159,7 @@ export const draw = function (text: string, id: string, _version: string, diagOb
     .attr('class', 'link')
     .style('mix-blend-mode', 'multiply');
 
-  const linkColor = conf?.linkColor || 'gradient';
+  const linkColor = conf?.linkColor ?? 'gradient';
 
   if (linkColor === 'gradient') {
     const gradient = link
diff --git a/packages/mermaid/src/diagrams/sequence/sequenceDb.ts b/packages/mermaid/src/diagrams/sequence/sequenceDb.ts
index 988db7f92..a0181d411 100644
--- a/packages/mermaid/src/diagrams/sequence/sequenceDb.ts
+++ b/packages/mermaid/src/diagrams/sequence/sequenceDb.ts
@@ -46,7 +46,7 @@ const state = new ImperativeState<SequenceState>(() => ({
 export const addBox = function (data: { text: string; color: string; wrap: boolean }) {
   state.records.boxes.push({
     name: data.text,
-    wrap: (data.wrap === undefined && autoWrap()) || !!data.wrap,
+    wrap: (data.wrap === undefined && autoWrap()) ?? !!data.wrap,
     fill: data.color,
     actorKeys: [],
   });
@@ -91,7 +91,7 @@ export const addActor = function (
     box: assignedBox,
     name: name,
     description: description.text,
-    wrap: (description.wrap === undefined && autoWrap()) || !!description.wrap,
+    wrap: (description.wrap === undefined && autoWrap()) ?? !!description.wrap,
     prevActor: state.records.prevActor,
     links: {},
     properties: {},
@@ -145,7 +145,7 @@ export const addMessage = function (
     from: idFrom,
     to: idTo,
     message: message.text,
-    wrap: (message.wrap === undefined && autoWrap()) || !!message.wrap,
+    wrap: (message.wrap === undefined && autoWrap()) ?? !!message.wrap,
     answer: answer,
   });
 };
@@ -158,7 +158,7 @@ export const addSignal = function (
   activate = false
 ) {
   if (messageType === LINETYPE.ACTIVE_END) {
-    const cnt = activationCount(idFrom || '');
+    const cnt = activationCount(idFrom ?? '');
     if (cnt < 1) {
       // Bail out as there is an activation signal from an inactive participant
       const error = new Error('Trying to inactivate an inactive participant (' + idFrom + ')');
@@ -178,7 +178,7 @@ export const addSignal = function (
     from: idFrom,
     to: idTo,
     message: message?.text ?? '',
-    wrap: (message?.wrap === undefined && autoWrap()) || !!message?.wrap,
+    wrap: (message?.wrap === undefined && autoWrap()) ?? !!message?.wrap,
     type: messageType,
     activate,
   });
@@ -352,7 +352,7 @@ export const addNote = function (
     actor: actor,
     placement: placement,
     message: message.text,
-    wrap: (message.wrap === undefined && autoWrap()) || !!message.wrap,
+    wrap: (message.wrap === undefined && autoWrap()) ?? !!message.wrap,
   };
 
   //@ts-ignore: Coerce actor into a [to, from, ...] array
@@ -363,7 +363,7 @@ export const addNote = function (
     from: actors[0],
     to: actors[1],
     message: message.text,
-    wrap: (message.wrap === undefined && autoWrap()) || !!message.wrap,
+    wrap: (message.wrap === undefined && autoWrap()) ?? !!message.wrap,
     type: LINETYPE.NOTE,
     placement: placement,
   });
diff --git a/packages/mermaid/src/diagrams/xychart/chartBuilder/components/axis/bandAxis.ts b/packages/mermaid/src/diagrams/xychart/chartBuilder/components/axis/bandAxis.ts
index 864ef1316..98eb31235 100644
--- a/packages/mermaid/src/diagrams/xychart/chartBuilder/components/axis/bandAxis.ts
+++ b/packages/mermaid/src/diagrams/xychart/chartBuilder/components/axis/bandAxis.ts
@@ -40,6 +40,6 @@ export class BandAxis extends BaseAxis {
   }
 
   getScaleValue(value: string): number {
-    return this.scale(value) || this.getRange()[0];
+    return this.scale(value) ?? this.getRange()[0];
   }
 }
diff --git a/packages/mermaid/src/mermaidAPI.ts b/packages/mermaid/src/mermaidAPI.ts
index ffd7d4bea..7bca4d995 100644
--- a/packages/mermaid/src/mermaidAPI.ts
+++ b/packages/mermaid/src/mermaidAPI.ts
@@ -128,7 +128,7 @@ export const createCssStyles = (
 
   // classDefs defined in the diagram text
   if (classDefs instanceof Map) {
-    const htmlLabels = config.htmlLabels || config.flowchart?.htmlLabels; // TODO why specifically check the Flowchart diagram config?
+    const htmlLabels = config.htmlLabels ?? config.flowchart?.htmlLabels; // TODO why specifically check the Flowchart diagram config?
 
     const cssHtmlElements = ['> *', 'span']; // TODO make a constant
     const cssShapeElements = ['rect', 'polygon', 'ellipse', 'circle', 'path']; // TODO make a constant