Add GetSafeProperty method to cmTarget, cmGeneratorTarget and cmSourceFile

Source/cmGeneratorTarget.cxx

@@ -221,6 +221,15 @@ const char* cmGeneratorTarget::GetProperty(const std::string& prop) const
   return this->Target->GetProperty(prop);
 }
 
+const char* cmGeneratorTarget::GetSafeProperty(const std::string& prop) const
+{
+  const char* ret = this->GetProperty(prop);
+  if (!ret) {
+    return "";
+  }
+  return ret;
+}
+
 const char* cmGeneratorTarget::GetOutputTargetType(
   cmStateEnums::ArtifactType artifact) const
 {

Source/cmGeneratorTarget.h

@@ -68,7 +68,10 @@ public:
   std::string GetExportName() const;
 
   std::vector<std::string> GetPropertyKeys() const;
+  ///! Might return a nullptr if the property is not set or invalid
   const char* GetProperty(const std::string& prop) const;
+  ///! Always returns a valid pointer
+  const char* GetSafeProperty(const std::string& prop) const;
   bool GetPropertyAsBool(const std::string& prop) const;
   void GetSourceFiles(std::vector<cmSourceFile*>& files,
                       const std::string& config) const;

Source/cmSourceFile.cxx

@@ -296,6 +296,15 @@ const char* cmSourceFile::GetProperty(const std::string& prop) const
   return retVal;
 }
 
+const char* cmSourceFile::GetSafeProperty(const std::string& prop) const
+{
+  const char* ret = this->GetProperty(prop);
+  if (!ret) {
+    return "";
+  }
+  return ret;
+}
+
 bool cmSourceFile::GetPropertyAsBool(const std::string& prop) const
 {
   return cmSystemTools::IsOn(this->GetProperty(prop));

Source/cmSourceFile.h

@@ -45,7 +45,10 @@ public:
   void SetProperty(const std::string& prop, const char* value);
   void AppendProperty(const std::string& prop, const char* value,
                       bool asString = false);
+  ///! Might return a nullptr if the property is not set or invalid
   const char* GetProperty(const std::string& prop) const;
+  ///! Always returns a valid pointer
+  const char* GetSafeProperty(const std::string& prop) const;
   bool GetPropertyAsBool(const std::string& prop) const;
 
   /** Implement getting a property when called from a CMake language

Source/cmTarget.cxx

@@ -1412,6 +1412,15 @@ const char* cmTarget::GetProperty(const std::string& prop) const
   return retVal;
 }
 
+const char* cmTarget::GetSafeProperty(const std::string& prop) const
+{
+  const char* ret = this->GetProperty(prop);
+  if (!ret) {
+    return "";
+  }
+  return ret;
+}
+
 bool cmTarget::GetPropertyAsBool(const std::string& prop) const
 {
   return cmSystemTools::IsOn(this->GetProperty(prop));

Source/cmTarget.h

@@ -200,7 +200,10 @@ public:
   void SetProperty(const std::string& prop, const char* value);
   void AppendProperty(const std::string& prop, const char* value,
                       bool asString = false);
+  ///! Might return a nullptr if the property is not set or invalid
   const char* GetProperty(const std::string& prop) const;
+  ///! Always returns a valid pointer
+  const char* GetSafeProperty(const std::string& prop) const;
   bool GetPropertyAsBool(const std::string& prop) const;
   void CheckProperty(const std::string& prop, cmMakefile* context) const;
   const char* GetComputedProperty(const std::string& prop,