Add some missing Nullable annotations.

PiperOrigin-RevId: 799527319
Change-Id: If84a3b2f19243ea9cf8b114d1421879d8186eb1d

doc/APIreference/functions.rst

@@ -1342,6 +1342,8 @@ Set default options for length range computation.
 
 Set solver parameters to default values.
 
+*Nullable:* ``solref``, ``solimp``
+
 .. _mj_defaultOption:
 
 `mj_defaultOption <#mj_defaultOption>`__
@@ -1369,6 +1371,8 @@ Set visual options to default values.
 
 Copy mjModel, allocate new if dest is NULL.
 
+*Nullable:* ``dest``
+
 .. _mj_saveModel:
 
 `mj_saveModel <#mj_saveModel>`__

include/mujoco/mujoco.h

@@ -166,6 +166,7 @@ MJAPI void mj_inverseSkip(const mjModel* m, mjData* d, int skipstage, int skipse
 MJAPI void mj_defaultLROpt(mjLROpt* opt);
 
 // Set solver parameters to default values.
+// Nullable: solref, solimp
 MJAPI void mj_defaultSolRefImp(mjtNum* solref, mjtNum* solimp);
 
 // Set physics options to default values.
@@ -175,6 +176,7 @@ MJAPI void mj_defaultOption(mjOption* opt);
 MJAPI void mj_defaultVisual(mjVisual* vis);
 
 // Copy mjModel, allocate new if dest is NULL.
+// Nullable: dest
 MJAPI mjModel* mj_copyModel(mjModel* dest, const mjModel* src);
 
 // Save model to binary MJB file or memory buffer; buffer has precedence when given.

python/mujoco/introspect/functions.py

@@ -592,12 +592,14 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
                  type=PointerType(
                      inner_type=ValueType(name='mjtNum'),
                  ),
+                 nullable=True,
              ),
              FunctionParameterDecl(
                  name='solimp',
                  type=PointerType(
                      inner_type=ValueType(name='mjtNum'),
                  ),
+                 nullable=True,
              ),
          ),
          doc='Set solver parameters to default values.',
@@ -642,6 +644,7 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
                  type=PointerType(
                      inner_type=ValueType(name='mjModel'),
                  ),
+                 nullable=True,
              ),
              FunctionParameterDecl(
                  name='src',