diff --git a/llvm/include/llvm/Support/YAMLTraits.h b/llvm/include/llvm/Support/YAMLTraits.h
--- a/llvm/include/llvm/Support/YAMLTraits.h
+++ b/llvm/include/llvm/Support/YAMLTraits.h
@@ -902,24 +902,7 @@
   template <typename T, typename Context>
   void processKeyWithDefault(const char *Key, Optional<T> &Val,
                              const Optional<T> &DefaultValue, bool Required,
-                             Context &Ctx) {
-    assert(DefaultValue.hasValue() == false &&
-           "Optional<T> shouldn't have a value!");
-    void *SaveInfo;
-    bool UseDefault = true;
-    const bool sameAsDefault = outputting() && !Val.hasValue();
-    if (!outputting() && !Val.hasValue())
-      Val = T();
-    if (Val.hasValue() &&
-        this->preflightKey(Key, Required, sameAsDefault, UseDefault,
-                           SaveInfo)) {
-      yamlize(*this, Val.getValue(), Required, Ctx);
-      this->postflightKey(SaveInfo);
-    } else {
-      if (UseDefault)
-        Val = DefaultValue;
-    }
-  }
+                             Context &Ctx);
 
   template <typename T, typename Context>
   void processKeyWithDefault(const char *Key, T &Val, const T &DefaultValue,
@@ -1625,6 +1608,40 @@
   StringRef PaddingBeforeContainer;
 };
 
+template <typename T, typename Context>
+void IO::processKeyWithDefault(const char *Key, Optional<T> &Val,
+                               const Optional<T> &DefaultValue, bool Required,
+                               Context &Ctx) {
+  assert(DefaultValue.hasValue() == false &&
+         "Optional<T> shouldn't have a value!");
+  void *SaveInfo;
+  bool UseDefault = true;
+  const bool sameAsDefault = outputting() && !Val.hasValue();
+  if (!outputting() && !Val.hasValue())
+    Val = T();
+  if (Val.hasValue() &&
+      this->preflightKey(Key, Required, sameAsDefault, UseDefault, SaveInfo)) {
+
+    // When reading an Optional<X> key from a YAML description, we allow the
+    // special "<none>" value, which can be used to specify that no value was
+    // requested, i.e. the DefaultValue will be assigned. The DefaultValue is
+    // usually None.
+    bool IsNone = false;
+    if (!outputting())
+      if (auto *Node = dyn_cast<ScalarNode>(((Input *)this)->getCurrentNode()))
+        IsNone = Node->getRawValue() == "<none>";
+
+    if (IsNone)
+      Val = DefaultValue;
+    else
+      yamlize(*this, Val.getValue(), Required, Ctx);
+    this->postflightKey(SaveInfo);
+  } else {
+    if (UseDefault)
+      Val = DefaultValue;
+  }
+}
+
 /// YAML I/O does conversion based on types. But often native data types
 /// are just a typedef of built in intergral types (e.g. int).  But the C++
 /// type matching system sees through the typedef and all the typedefed types
diff --git a/llvm/test/tools/yaml2obj/ELF/none-value.yaml b/llvm/test/tools/yaml2obj/ELF/none-value.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/yaml2obj/ELF/none-value.yaml
@@ -0,0 +1,45 @@
+## We have a special "<none>" value for all keys that are implemented
+## as Optional<> in the code. Setting a key to "<none>" means no-op and
+## works in the same way as when a field was not specified at all.
+
+## Test a few keys for which the "<none>" value is supported.
+## We do not test all possible keys, because it would be too verbose.
+## It reasonable to test all keys for a section, because normally many
+## of them would conflict or intersect when specified together.
+# RUN: yaml2obj %s --docnum=1 -o %t-none
+# RUN: yaml2obj %s --docnum=2 -o %t-base
+# RUN: cmp %t-none %t-base
+
+## We do not use the TEST macro. It exists to
+## demonstrate the expected use case for the <none> word.
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:         .bar
+    Type:         SHT_PROGBITS
+    Offset:       [[TEST=<none>]]
+    Address:      [[TEST=<none>]]
+    Content:      [[TEST=<none>]]
+    Size:         [[TEST=<none>]]
+    ContentArray: [[TEST=<none>]]
+    Info:         [[TEST=<none>]]
+    EntSize:      [[TEST=<none>]]
+    ShName:       [[TEST=<none>]]
+    ShOffset:     [[TEST=<none>]]
+    ShSize:       [[TEST=<none>]]
+    ShFlags:      [[TEST=<none>]]
+
+## The same document, but all fields that were set to <none> are removed.
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name: .bar
+    Type: SHT_PROGBITS