diff --git a/gobject/gsignal.c b/gobject/gsignal.c
index 41599eb0d..81d2834b9 100644
--- a/gobject/gsignal.c
+++ b/gobject/gsignal.c
@@ -1035,9 +1035,9 @@ signal_finalize_hook (GHookList *hook_list,
  * g_signal_add_emission_hook:
  * @signal_id: the signal identifier, as returned by g_signal_lookup().
  * @detail: the detail on which to call the hook.
- * @hook_func: a #GSignalEmissionHook function.
- * @hook_data: user data for @hook_func.
- * @data_destroy: a #GDestroyNotify for @hook_data.
+ * @hook_func: (not nullable): a #GSignalEmissionHook function.
+ * @hook_data: (nullable): user data for @hook_func.
+ * @data_destroy: (nullable): a #GDestroyNotify for @hook_data.
  *
  * Adds an emission hook for a signal, which will get called for any emission
  * of that signal, independent of the instance. This is possible only
@@ -1389,7 +1389,7 @@ g_signal_list_ids (GType  itype,
  *
  * Two different signals may have the same name, if they have differing types.
  *
- * Returns: the signal name, or %NULL if the signal number was invalid.
+ * Returns: (nullable): the signal name, or %NULL if the signal number was invalid.
  */
 const gchar *
 g_signal_name (guint signal_id)
@@ -1408,7 +1408,7 @@ g_signal_name (guint signal_id)
 /**
  * g_signal_query:
  * @signal_id: The signal id of the signal to query information for.
- * @query: (out caller-allocates): A user provided structure that is
+ * @query: (out caller-allocates) (not optional): A user provided structure that is
  *  filled in with constant values upon success.
  *
  * Queries the signal system for in-depth information about a
@@ -1454,8 +1454,8 @@ g_signal_query (guint         signal_id,
  * @class_offset: The offset of the function pointer in the class structure
  *  for this type. Used to invoke a class method generically. Pass 0 to
  *  not associate a class method slot with this signal.
- * @accumulator: the accumulator for this signal; may be %NULL.
- * @accu_data: user data for the @accumulator.
+ * @accumulator: (nullable): the accumulator for this signal; may be %NULL.
+ * @accu_data: (nullable): user data for the @accumulator.
  * @c_marshaller: (nullable): the function to translate arrays of parameter
  *  values to signal emissions into C language callback invocations or %NULL.
  * @return_type: the type of return value, or #G_TYPE_NONE for a signal
@@ -1527,11 +1527,11 @@ g_signal_new (const gchar	 *signal_name,
  * @signal_flags: a combination of #GSignalFlags specifying detail of when
  *  the default handler is to be invoked. You should at least specify
  *  %G_SIGNAL_RUN_FIRST or %G_SIGNAL_RUN_LAST.
- * @class_handler: a #GCallback which acts as class implementation of
+ * @class_handler: (nullable): a #GCallback which acts as class implementation of
  *  this signal. Used to invoke a class method generically. Pass %NULL to
  *  not associate a class method with this signal.
- * @accumulator: the accumulator for this signal; may be %NULL.
- * @accu_data: user data for the @accumulator.
+ * @accumulator: (nullable): the accumulator for this signal; may be %NULL.
+ * @accu_data: (nullable): user data for the @accumulator.
  * @c_marshaller: (nullable): the function to translate arrays of parameter
  *  values to signal emissions into C language callback invocations or %NULL.
  * @return_type: the type of return value, or #G_TYPE_NONE for a signal
@@ -1668,15 +1668,15 @@ signal_add_class_closure (SignalNode *node,
  * @class_closure: (nullable): The closure to invoke on signal emission;
  *     may be %NULL
  * @accumulator: (nullable): the accumulator for this signal; may be %NULL
- * @accu_data: user data for the @accumulator
+ * @accu_data: (nullable): user data for the @accumulator
  * @c_marshaller: (nullable): the function to translate arrays of
  *     parameter values to signal emissions into C language callback
  *     invocations or %NULL
  * @return_type: the type of return value, or #G_TYPE_NONE for a signal
  *     without a return value
  * @n_params: the length of @param_types
- * @param_types: (array length=n_params): an array of types, one for
- *     each parameter
+ * @param_types: (array length=n_params) (nullable): an array of types, one for
+ *     each parameter (may be %NULL if @n_params is zero)
  *
  * Creates a new signal. (This is usually done in the class initializer.)
  *
@@ -1935,9 +1935,9 @@ g_signal_set_va_marshaller (guint              signal_id,
  * @signal_flags: a combination of #GSignalFlags specifying detail of when
  *  the default handler is to be invoked. You should at least specify
  *  %G_SIGNAL_RUN_FIRST or %G_SIGNAL_RUN_LAST.
- * @class_closure: The closure to invoke on signal emission; may be %NULL.
- * @accumulator: the accumulator for this signal; may be %NULL.
- * @accu_data: user data for the @accumulator.
+ * @class_closure: (nullable): The closure to invoke on signal emission; may be %NULL.
+ * @accumulator: (nullable): the accumulator for this signal; may be %NULL.
+ * @accu_data: (nullable): user data for the @accumulator.
  * @c_marshaller: (nullable): the function to translate arrays of parameter
  *  values to signal emissions into C language callback invocations or %NULL.
  * @return_type: the type of return value, or #G_TYPE_NONE for a signal
@@ -2366,7 +2366,8 @@ g_signal_chain_from_overridden_handler (gpointer instance,
  *
  * Returns the invocation hint of the innermost signal emission of instance.
  *
- * Returns: (transfer none): the invocation hint of the innermost signal  emission.
+ * Returns: (transfer none) (nullable): the invocation hint of the innermost
+ *     signal emission, or %NULL if not found.
  */
 GSignalInvocationHint*
 g_signal_get_invocation_hint (gpointer instance)
@@ -2387,7 +2388,7 @@ g_signal_get_invocation_hint (gpointer instance)
  * @instance: (type GObject.Object): the instance to connect to.
  * @signal_id: the id of the signal.
  * @detail: the detail.
- * @closure: the closure to connect.
+ * @closure: (not nullable): the closure to connect.
  * @after: whether the handler should be called before or after the
  *  default handler of the signal.
  *
@@ -2449,7 +2450,7 @@ g_signal_connect_closure_by_id (gpointer  instance,
  * g_signal_connect_closure:
  * @instance: (type GObject.Object): the instance to connect to.
  * @detailed_signal: a string of the form "signal-name::detail".
- * @closure: the closure to connect.
+ * @closure: (not nullable): the closure to connect.
  * @after: whether the handler should be called before or after the
  *  default handler of the signal.
  *
@@ -2540,9 +2541,9 @@ node_check_deprecated (const SignalNode *node)
  * g_signal_connect_data:
  * @instance: (type GObject.Object): the instance to connect to.
  * @detailed_signal: a string of the form "signal-name::detail".
- * @c_handler: the #GCallback to connect.
- * @data: data to pass to @c_handler calls.
- * @destroy_data: a #GClosureNotify for @data.
+ * @c_handler: (not nullable): the #GCallback to connect.
+ * @data: (nullable): data to pass to @c_handler calls.
+ * @destroy_data: (nullable): a #GClosureNotify for @data.
  * @connect_flags: a combination of #GConnectFlags.
  *
  * Connects a #GCallback function to a signal for a particular object. Similar
@@ -2819,7 +2820,7 @@ g_signal_handlers_destroy (gpointer instance)
  * @detail: Signal detail the handler has to be connected to.
  * @closure: (nullable): The closure the handler will invoke.
  * @func: The C closure callback of the handler (useless for non-C closures).
- * @data: The closure data of the handler's closure.
+ * @data: (nullable): The closure data of the handler's closure.
  *
  * Finds the first signal handler that matches certain selection criteria.
  * The criteria mask is passed as an OR-ed combination of #GSignalMatchType
@@ -2899,7 +2900,7 @@ signal_handlers_foreach_matched_R (gpointer         instance,
  * @detail: Signal detail the handlers have to be connected to.
  * @closure: (nullable): The closure the handlers will invoke.
  * @func: The C closure callback of the handlers (useless for non-C closures).
- * @data: The closure data of the handlers' closures.
+ * @data: (nullable): The closure data of the handlers' closures.
  *
  * Blocks all handlers on an instance that match a certain selection criteria.
  * The criteria mask is passed as an OR-ed combination of #GSignalMatchType
@@ -2946,7 +2947,7 @@ g_signal_handlers_block_matched (gpointer         instance,
  * @detail: Signal detail the handlers have to be connected to.
  * @closure: (nullable): The closure the handlers will invoke.
  * @func: The C closure callback of the handlers (useless for non-C closures).
- * @data: The closure data of the handlers' closures.
+ * @data: (nullable): The closure data of the handlers' closures.
  *
  * Unblocks all handlers on an instance that match a certain selection
  * criteria. The criteria mask is passed as an OR-ed combination of
@@ -2994,7 +2995,7 @@ g_signal_handlers_unblock_matched (gpointer         instance,
  * @detail: Signal detail the handlers have to be connected to.
  * @closure: (nullable): The closure the handlers will invoke.
  * @func: The C closure callback of the handlers (useless for non-C closures).
- * @data: The closure data of the handlers' closures.
+ * @data: (nullable): The closure data of the handlers' closures.
  *
  * Disconnects all handlers on an instance that match a certain
  * selection criteria. The criteria mask is passed as an OR-ed