diff --git a/src/embed_tests/TestPyObject.cs b/src/embed_tests/TestPyObject.cs
index 65ac20e9a..d4952d4a3 100644
--- a/src/embed_tests/TestPyObject.cs
+++ b/src/embed_tests/TestPyObject.cs
@@ -57,5 +57,11 @@ def add(self, x, y):
                 Assert.IsTrue(memberNames.Contains(expectedName), "Could not find member '{0}'.", expectedName);
             }
         }
+
+        [Test]
+        public void InvokeNull() {
+            var list = PythonEngine.Eval("list");
+            Assert.Throws<ArgumentNullException>(() => list.Invoke(new PyObject[] {null}));
+        }
     }
 }
diff --git a/src/runtime/pyint.cs b/src/runtime/pyint.cs
index f6911d9d7..217cf7e20 100644
--- a/src/runtime/pyint.cs
+++ b/src/runtime/pyint.cs
@@ -62,7 +62,7 @@ public PyInt(int value)
         /// Creates a new Python int from a uint32 value.
         /// </remarks>
         [CLSCompliant(false)]
-        public PyInt(uint value) : base(IntPtr.Zero)
+        public PyInt(uint value)
         {
             obj = Runtime.PyInt_FromInt64(value);
             Runtime.CheckExceptionOccurred();
@@ -75,7 +75,7 @@ public PyInt(uint value) : base(IntPtr.Zero)
         /// <remarks>
         /// Creates a new Python int from an int64 value.
         /// </remarks>
-        public PyInt(long value) : base(IntPtr.Zero)
+        public PyInt(long value)
         {
             obj = Runtime.PyInt_FromInt64(value);
             Runtime.CheckExceptionOccurred();
@@ -89,7 +89,7 @@ public PyInt(long value) : base(IntPtr.Zero)
         /// Creates a new Python int from a uint64 value.
         /// </remarks>
         [CLSCompliant(false)]
-        public PyInt(ulong value) : base(IntPtr.Zero)
+        public PyInt(ulong value)
         {
             obj = Runtime.PyInt_FromInt64((long)value);
             Runtime.CheckExceptionOccurred();
diff --git a/src/runtime/pyobject.cs b/src/runtime/pyobject.cs
index c86504802..8ae99ecd0 100644
--- a/src/runtime/pyobject.cs
+++ b/src/runtime/pyobject.cs
@@ -3,6 +3,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Dynamic;
+using System.Linq;
 using System.Linq.Expressions;
 
 namespace Python.Runtime
@@ -43,6 +44,8 @@ public class PyObject : DynamicObject, IEnumerable, IPyDisposable
         /// </remarks>
         public PyObject(IntPtr ptr)
         {
+            if (ptr == IntPtr.Zero) throw new ArgumentNullException(nameof(ptr));
+
             obj = ptr;
 #if TRACE_ALLOC
             Traceback = new StackTrace(1);
@@ -51,7 +54,7 @@ public PyObject(IntPtr ptr)
 
         // Protected default constructor to allow subclasses to manage
         // initialization in different ways as appropriate.
-
+        [Obsolete("Please, always use PyObject(IntPtr)")]
         protected PyObject()
         {
 #if TRACE_ALLOC
@@ -209,6 +212,8 @@ public PyObject GetPythonType()
         /// </remarks>
         public bool TypeCheck(PyObject typeOrClass)
         {
+            if (typeOrClass == null) throw new ArgumentNullException(nameof(typeOrClass));
+
             return Runtime.PyObject_TypeCheck(obj, typeOrClass.obj);
         }
 
@@ -221,6 +226,8 @@ public bool TypeCheck(PyObject typeOrClass)
         /// </remarks>
         public bool HasAttr(string name)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             return Runtime.PyObject_HasAttrString(obj, name) != 0;
         }
 
@@ -234,6 +241,8 @@ public bool HasAttr(string name)
         /// </remarks>
         public bool HasAttr(PyObject name)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             return Runtime.PyObject_HasAttr(obj, name.obj) != 0;
         }
 
@@ -247,6 +256,8 @@ public bool HasAttr(PyObject name)
         /// </remarks>
         public PyObject GetAttr(string name)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             IntPtr op = Runtime.PyObject_GetAttrString(obj, name);
             if (op == IntPtr.Zero)
             {
@@ -257,7 +268,7 @@ public PyObject GetAttr(string name)
 
 
         /// <summary>
-        /// GetAttr Method
+        /// GetAttr Method. Returns fallback value if getting attribute fails for any reason.
         /// </summary>
         /// <remarks>
         /// Returns the named attribute of the Python object, or the given
@@ -265,6 +276,8 @@ public PyObject GetAttr(string name)
         /// </remarks>
         public PyObject GetAttr(string name, PyObject _default)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             IntPtr op = Runtime.PyObject_GetAttrString(obj, name);
             if (op == IntPtr.Zero)
             {
@@ -285,6 +298,8 @@ public PyObject GetAttr(string name, PyObject _default)
         /// </remarks>
         public PyObject GetAttr(PyObject name)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             IntPtr op = Runtime.PyObject_GetAttr(obj, name.obj);
             if (op == IntPtr.Zero)
             {
@@ -304,6 +319,8 @@ public PyObject GetAttr(PyObject name)
         /// </remarks>
         public PyObject GetAttr(PyObject name, PyObject _default)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             IntPtr op = Runtime.PyObject_GetAttr(obj, name.obj);
             if (op == IntPtr.Zero)
             {
@@ -323,6 +340,9 @@ public PyObject GetAttr(PyObject name, PyObject _default)
         /// </remarks>
         public void SetAttr(string name, PyObject value)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
             int r = Runtime.PyObject_SetAttrString(obj, name, value.obj);
             if (r < 0)
             {
@@ -341,6 +361,9 @@ public void SetAttr(string name, PyObject value)
         /// </remarks>
         public void SetAttr(PyObject name, PyObject value)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
             int r = Runtime.PyObject_SetAttr(obj, name.obj, value.obj);
             if (r < 0)
             {
@@ -358,6 +381,8 @@ public void SetAttr(PyObject name, PyObject value)
         /// </remarks>
         public void DelAttr(string name)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             int r = Runtime.PyObject_SetAttrString(obj, name, IntPtr.Zero);
             if (r < 0)
             {
@@ -376,6 +401,8 @@ public void DelAttr(string name)
         /// </remarks>
         public void DelAttr(PyObject name)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+
             int r = Runtime.PyObject_SetAttr(obj, name.obj, IntPtr.Zero);
             if (r < 0)
             {
@@ -394,6 +421,8 @@ public void DelAttr(PyObject name)
         /// </remarks>
         public virtual PyObject GetItem(PyObject key)
         {
+            if (key == null) throw new ArgumentNullException(nameof(key));
+
             IntPtr op = Runtime.PyObject_GetItem(obj, key.obj);
             if (op == IntPtr.Zero)
             {
@@ -413,6 +442,8 @@ public virtual PyObject GetItem(PyObject key)
         /// </remarks>
         public virtual PyObject GetItem(string key)
         {
+            if (key == null) throw new ArgumentNullException(nameof(key));
+
             using (var pyKey = new PyString(key))
             {
                 return GetItem(pyKey);
@@ -447,6 +478,9 @@ public virtual PyObject GetItem(int index)
         /// </remarks>
         public virtual void SetItem(PyObject key, PyObject value)
         {
+            if (key == null) throw new ArgumentNullException(nameof(key));
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
             int r = Runtime.PyObject_SetItem(obj, key.obj, value.obj);
             if (r < 0)
             {
@@ -465,6 +499,9 @@ public virtual void SetItem(PyObject key, PyObject value)
         /// </remarks>
         public virtual void SetItem(string key, PyObject value)
         {
+            if (key == null) throw new ArgumentNullException(nameof(key));
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
             using (var pyKey = new PyString(key))
             {
                 SetItem(pyKey, value);
@@ -482,6 +519,8 @@ public virtual void SetItem(string key, PyObject value)
         /// </remarks>
         public virtual void SetItem(int index, PyObject value)
         {
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
             using (var pyindex = new PyInt(index))
             {
                 SetItem(pyindex, value);
@@ -499,6 +538,8 @@ public virtual void SetItem(int index, PyObject value)
         /// </remarks>
         public virtual void DelItem(PyObject key)
         {
+            if (key == null) throw new ArgumentNullException(nameof(key));
+
             int r = Runtime.PyObject_DelItem(obj, key.obj);
             if (r < 0)
             {
@@ -517,6 +558,8 @@ public virtual void DelItem(PyObject key)
         /// </remarks>
         public virtual void DelItem(string key)
         {
+            if (key == null) throw new ArgumentNullException(nameof(key));
+
             using (var pyKey = new PyString(key))
             {
                 DelItem(pyKey);
@@ -639,10 +682,13 @@ public IEnumerator GetEnumerator()
         /// </summary>
         /// <remarks>
         /// Invoke the callable object with the given arguments, passed as a
-        /// PyObject[]. A PythonException is raised if the invokation fails.
+        /// PyObject[]. A PythonException is raised if the invocation fails.
         /// </remarks>
         public PyObject Invoke(params PyObject[] args)
         {
+            if (args == null) throw new ArgumentNullException(nameof(args));
+            if (args.Contains(null)) throw new ArgumentNullException();
+
             var t = new PyTuple(args);
             IntPtr r = Runtime.PyObject_Call(obj, t.obj, IntPtr.Zero);
             t.Dispose();
@@ -659,10 +705,12 @@ public PyObject Invoke(params PyObject[] args)
         /// </summary>
         /// <remarks>
         /// Invoke the callable object with the given arguments, passed as a
-        /// Python tuple. A PythonException is raised if the invokation fails.
+        /// Python tuple. A PythonException is raised if the invocation fails.
         /// </remarks>
         public PyObject Invoke(PyTuple args)
         {
+            if (args == null) throw new ArgumentNullException(nameof(args));
+
             IntPtr r = Runtime.PyObject_Call(obj, args.obj, IntPtr.Zero);
             if (r == IntPtr.Zero)
             {
@@ -677,12 +725,15 @@ public PyObject Invoke(PyTuple args)
         /// </summary>
         /// <remarks>
         /// Invoke the callable object with the given positional and keyword
-        /// arguments. A PythonException is raised if the invokation fails.
+        /// arguments. A PythonException is raised if the invocation fails.
         /// </remarks>
         public PyObject Invoke(PyObject[] args, PyDict kw)
         {
+            if (args == null) throw new ArgumentNullException(nameof(args));
+            if (args.Contains(null)) throw new ArgumentNullException();
+
             var t = new PyTuple(args);
-            IntPtr r = Runtime.PyObject_Call(obj, t.obj, kw != null ? kw.obj : IntPtr.Zero);
+            IntPtr r = Runtime.PyObject_Call(obj, t.obj, kw?.obj ?? IntPtr.Zero);
             t.Dispose();
             if (r == IntPtr.Zero)
             {
@@ -697,11 +748,13 @@ public PyObject Invoke(PyObject[] args, PyDict kw)
         /// </summary>
         /// <remarks>
         /// Invoke the callable object with the given positional and keyword
-        /// arguments. A PythonException is raised if the invokation fails.
+        /// arguments. A PythonException is raised if the invocation fails.
         /// </remarks>
         public PyObject Invoke(PyTuple args, PyDict kw)
         {
-            IntPtr r = Runtime.PyObject_Call(obj, args.obj, kw != null ? kw.obj : IntPtr.Zero);
+            if (args == null) throw new ArgumentNullException(nameof(args));
+
+            IntPtr r = Runtime.PyObject_Call(obj, args.obj, kw?.obj ?? IntPtr.Zero);
             if (r == IntPtr.Zero)
             {
                 throw new PythonException();
@@ -715,10 +768,14 @@ public PyObject Invoke(PyTuple args, PyDict kw)
         /// </summary>
         /// <remarks>
         /// Invoke the named method of the object with the given arguments.
-        /// A PythonException is raised if the invokation is unsuccessful.
+        /// A PythonException is raised if the invocation is unsuccessful.
         /// </remarks>
         public PyObject InvokeMethod(string name, params PyObject[] args)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (args == null) throw new ArgumentNullException(nameof(args));
+            if (args.Contains(null)) throw new ArgumentNullException();
+
             PyObject method = GetAttr(name);
             PyObject result = method.Invoke(args);
             method.Dispose();
@@ -731,10 +788,51 @@ public PyObject InvokeMethod(string name, params PyObject[] args)
         /// </summary>
         /// <remarks>
         /// Invoke the named method of the object with the given arguments.
-        /// A PythonException is raised if the invokation is unsuccessful.
+        /// A PythonException is raised if the invocation is unsuccessful.
         /// </remarks>
         public PyObject InvokeMethod(string name, PyTuple args)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (args == null) throw new ArgumentNullException(nameof(args));
+
+            PyObject method = GetAttr(name);
+            PyObject result = method.Invoke(args);
+            method.Dispose();
+            return result;
+        }
+
+        /// <summary>
+        /// InvokeMethod Method
+        /// </summary>
+        /// <remarks>
+        /// Invoke the named method of the object with the given arguments.
+        /// A PythonException is raised if the invocation is unsuccessful.
+        /// </remarks>
+        public PyObject InvokeMethod(PyObject name, params PyObject[] args)
+        {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (args == null) throw new ArgumentNullException(nameof(args));
+            if (args.Contains(null)) throw new ArgumentNullException();
+
+            PyObject method = GetAttr(name);
+            PyObject result = method.Invoke(args);
+            method.Dispose();
+            return result;
+        }
+
+
+        /// <summary>
+        /// InvokeMethod Method
+        /// </summary>
+        /// <remarks>
+        /// Invoke the named method of the object with the given arguments.
+        /// A PythonException is raised if the invocation is unsuccessful.
+        /// </remarks>
+        public PyObject InvokeMethod(PyObject name, PyTuple args)
+        {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (args == null) throw new ArgumentNullException(nameof(args));
+
             PyObject method = GetAttr(name);
             PyObject result = method.Invoke(args);
             method.Dispose();
@@ -748,10 +846,14 @@ public PyObject InvokeMethod(string name, PyTuple args)
         /// <remarks>
         /// Invoke the named method of the object with the given arguments
         /// and keyword arguments. Keyword args are passed as a PyDict object.
-        /// A PythonException is raised if the invokation is unsuccessful.
+        /// A PythonException is raised if the invocation is unsuccessful.
         /// </remarks>
         public PyObject InvokeMethod(string name, PyObject[] args, PyDict kw)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (args == null) throw new ArgumentNullException(nameof(args));
+            if (args.Contains(null)) throw new ArgumentNullException();
+
             PyObject method = GetAttr(name);
             PyObject result = method.Invoke(args, kw);
             method.Dispose();
@@ -765,10 +867,13 @@ public PyObject InvokeMethod(string name, PyObject[] args, PyDict kw)
         /// <remarks>
         /// Invoke the named method of the object with the given arguments
         /// and keyword arguments. Keyword args are passed as a PyDict object.
-        /// A PythonException is raised if the invokation is unsuccessful.
+        /// A PythonException is raised if the invocation is unsuccessful.
         /// </remarks>
         public PyObject InvokeMethod(string name, PyTuple args, PyDict kw)
         {
+            if (name == null) throw new ArgumentNullException(nameof(name));
+            if (args == null) throw new ArgumentNullException(nameof(args));
+
             PyObject method = GetAttr(name);
             PyObject result = method.Invoke(args, kw);
             method.Dispose();
@@ -785,6 +890,8 @@ public PyObject InvokeMethod(string name, PyTuple args, PyDict kw)
         /// </remarks>
         public bool IsInstance(PyObject typeOrClass)
         {
+            if (typeOrClass == null) throw new ArgumentNullException(nameof(typeOrClass));
+
             int r = Runtime.PyObject_IsInstance(obj, typeOrClass.obj);
             if (r < 0)
             {
@@ -804,6 +911,8 @@ public bool IsInstance(PyObject typeOrClass)
         /// </remarks>
         public bool IsSubclass(PyObject typeOrClass)
         {
+            if (typeOrClass == null) throw new ArgumentNullException(nameof(typeOrClass));
+
             int r = Runtime.PyObject_IsSubclass(obj, typeOrClass.obj);
             if (r < 0)
             {