From f2bd7b16c28abfd6b171b01cffaa770057aa523f Mon Sep 17 00:00:00 2001
From: Olivier Couet <olivier.couet@gmail.com>
Date: Tue, 24 Feb 2026 14:43:10 +0100
Subject: [PATCH 1/2] Allow to create a TGraph2D with 0 points

---
 hist/hist/src/TGraph2D.cxx | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/hist/hist/src/TGraph2D.cxx b/hist/hist/src/TGraph2D.cxx
index 43dd758ce9bc8..6fd4198beb2e4 100644
--- a/hist/hist/src/TGraph2D.cxx
+++ b/hist/hist/src/TGraph2D.cxx
@@ -598,7 +598,7 @@ TGraph2D& TGraph2D::operator=(const TGraph2D &g)
 
 void TGraph2D::Build(Int_t n)
 {
-   if (n <= 0) {
+   if (n < 0) {
       Error("TGraph2D", "Invalid number of points (%d)", n);
       return;
    }
@@ -609,12 +609,18 @@ void TGraph2D::Build(Int_t n)
    fNpy       = 40;
    fDirectory = nullptr;
    fHistogram = nullptr;
-   fDelaunay = nullptr;
+   fDelaunay  = nullptr;
    fMaximum   = -1111;
    fMinimum   = -1111;
-   fX         = new Double_t[fSize];
-   fY         = new Double_t[fSize];
-   fZ         = new Double_t[fSize];
+   if (n>0) {
+      fX = new Double_t[fSize];
+      fY = new Double_t[fSize];
+      fZ = new Double_t[fSize];
+   } else {
+      fX = nullptr;
+      fY = nullptr;
+      fZ = nullptr;
+   }
    fZout      = 0;
    fMaxIter   = 100000;
    fFunctions = new TList;

From dd045915b2b535304e9ce64637e77f11cf9acc49 Mon Sep 17 00:00:00 2001
From: Olivier Couet <olivier.couet@gmail.com>
Date: Tue, 24 Feb 2026 16:16:21 +0100
Subject: [PATCH 2/2] Does the same for the others TGraph2D classes.

---
 hist/hist/src/TGraph2DAsymmErrors.cxx | 46 +++++++++++++++++++--------
 hist/hist/src/TGraph2DErrors.cxx      | 28 +++++++++++-----
 2 files changed, 52 insertions(+), 22 deletions(-)

diff --git a/hist/hist/src/TGraph2DAsymmErrors.cxx b/hist/hist/src/TGraph2DAsymmErrors.cxx
index 6c659ac775773..965b4ad82e4ec 100644
--- a/hist/hist/src/TGraph2DAsymmErrors.cxx
+++ b/hist/hist/src/TGraph2DAsymmErrors.cxx
@@ -82,17 +82,26 @@ TGraph2DAsymmErrors::TGraph2DAsymmErrors() {}
 TGraph2DAsymmErrors::TGraph2DAsymmErrors(Int_t n)
                : TGraph2D(n)
 {
-   if (n <= 0) {
+   if (n < 0) {
       Error("TGraph2DAsymmErrors", "Invalid number of points (%d)", n);
       return;
    }
 
-   fEXlow  = new Double_t[n];
-   fEXhigh = new Double_t[n];
-   fEYlow  = new Double_t[n];
-   fEYhigh = new Double_t[n];
-   fEZlow  = new Double_t[n];
-   fEZhigh = new Double_t[n];
+   if (n>0) {
+      fEXlow  = new Double_t[n];
+      fEXhigh = new Double_t[n];
+      fEYlow  = new Double_t[n];
+      fEYhigh = new Double_t[n];
+      fEZlow  = new Double_t[n];
+      fEZhigh = new Double_t[n];
+   } else {
+      fEXlow  = nullptr;
+      fEXhigh = nullptr;
+      fEYlow  = nullptr;
+      fEYhigh = nullptr;
+      fEZlow  = nullptr;
+      fEZhigh = nullptr;
+   }
 
    for (Int_t i=0;i<n;i++) {
       fEXlow[i]  = 0;
@@ -111,17 +120,26 @@ TGraph2DAsymmErrors::TGraph2DAsymmErrors(Int_t n)
 TGraph2DAsymmErrors::TGraph2DAsymmErrors(Int_t n, Double_t *x, Double_t *y, Double_t *z, Double_t *exl, Double_t *exh, Double_t *eyl, Double_t *eyh, Double_t *ezl, Double_t *ezh,  Option_t *)
                :TGraph2D(n, x, y, z)
 {
-   if (n <= 0) {
+   if (n < 0) {
       Error("TGraph2DAsymmErrorsErrors", "Invalid number of points (%d)", n);
       return;
    }
 
-   fEXlow  = new Double_t[n];
-   fEXhigh = new Double_t[n];
-   fEYlow  = new Double_t[n];
-   fEYhigh = new Double_t[n];
-   fEZlow  = new Double_t[n];
-   fEZhigh = new Double_t[n];
+   if (n>0) {
+      fEXlow  = new Double_t[n];
+      fEXhigh = new Double_t[n];
+      fEYlow  = new Double_t[n];
+      fEYhigh = new Double_t[n];
+      fEZlow  = new Double_t[n];
+      fEZhigh = new Double_t[n];
+   } else {
+      fEXlow  = nullptr;
+      fEXhigh = nullptr;
+      fEYlow  = nullptr;
+      fEYhigh = nullptr;
+      fEZlow  = nullptr;
+      fEZhigh = nullptr;
+   }
 
    for (Int_t i=0;i<n;i++) {
       if (exl) fEXlow[i]  = exl[i];
diff --git a/hist/hist/src/TGraph2DErrors.cxx b/hist/hist/src/TGraph2DErrors.cxx
index b1bc4afa537f6..ef3e54d58bdbe 100644
--- a/hist/hist/src/TGraph2DErrors.cxx
+++ b/hist/hist/src/TGraph2DErrors.cxx
@@ -78,14 +78,20 @@ TGraph2DErrors::TGraph2DErrors() {}
 TGraph2DErrors::TGraph2DErrors(Int_t n)
                : TGraph2D(n)
 {
-   if (n <= 0) {
+   if (n < 0) {
       Error("TGraph2DErrors", "Invalid number of points (%d)", n);
       return;
    }
 
-   fEX = new Double_t[n];
-   fEY = new Double_t[n];
-   fEZ = new Double_t[n];
+   if (n>0) {
+      fEX = new Double_t[n];
+      fEY = new Double_t[n];
+      fEZ = new Double_t[n];
+   } else {
+      fEX = nullptr;
+      fEY = nullptr;
+      fEZ = nullptr;
+   }
 
    for (Int_t i=0;i<n;i++) {
       fEX[i] = 0;
@@ -102,14 +108,20 @@ TGraph2DErrors::TGraph2DErrors(Int_t n, Double_t *x, Double_t *y, Double_t *z,
                                Double_t *ex, Double_t *ey, Double_t *ez, Option_t *)
                :TGraph2D(n, x, y, z)
 {
-   if (n <= 0) {
+   if (n < 0) {
       Error("TGraph2DErrors", "Invalid number of points (%d)", n);
       return;
    }
 
-   fEX = new Double_t[n];
-   fEY = new Double_t[n];
-   fEZ = new Double_t[n];
+   if (n>0) {
+      fEX = new Double_t[n];
+      fEY = new Double_t[n];
+      fEZ = new Double_t[n];
+   } else {
+      fEX = nullptr;
+      fEY = nullptr;
+      fEZ = nullptr;
+   }
 
    for (Int_t i=0;i<n;i++) {
       if (ex) fEX[i] = ex[i];