[Java.Interop] Fix C# warnings (#652)

Fixes 43 Nullable Reference Type warnings

Fixes CS0168 warning:

	The variable 'e' is declared but never used.

Fixes 6 CA1307 warnings introduced by targeting `netcoreapp3.1`:

	The behavior of 'string.IndexOf(char)' could vary based on the current user's locale settings.

Author: jpobst

src/Java.Interop/Java.Interop/JavaArray.cs

@@ -258,31 +258,31 @@ bool ICollection<T>.Remove (T item)
 			throw new NotSupportedException ();
 		}
 
-		bool IList.Contains (object value)
+		bool IList.Contains (object? value)
 		{
 			if (value is T)
 				return Contains ((T) value);
 			return false;
 		}
 
-		int IList.IndexOf (object value)
+		int IList.IndexOf (object? value)
 		{
 			if (value is T)
 				return IndexOf ((T) value);
 			return -1;
 		}
 
-		int IList.Add (object value)
+		int IList.Add (object? value)
 		{
 			throw new NotSupportedException ();
 		}
 
-		void IList.Insert (int index, object value)
+		void IList.Insert (int index, object? value)
 		{
 			throw new NotSupportedException ();
 		}
 
-		void IList.Remove (object value)
+		void IList.Remove (object? value)
 		{
 			throw new NotSupportedException ();
 		}

src/Java.Interop/Java.Interop/JavaException.cs

@@ -162,7 +162,7 @@ protected virtual void Dispose (bool disposing)
 			}
 		}
 
-		public override bool Equals (object obj)
+		public override bool Equals (object? obj)
 		{
 			JniPeerMembers.AssertSelf (this);
 

src/Java.Interop/Java.Interop/JavaObject.cs

@@ -110,7 +110,7 @@ protected virtual void Dispose (bool disposing)
 		{
 		}
 
-		public override bool Equals (object obj)
+		public override bool Equals (object? obj)
 		{
 			JniPeerMembers.AssertSelf (this);
 

src/Java.Interop/Java.Interop/JavaPrimitiveArrays.cs

@@ -7,6 +7,7 @@
 
 using Java.Interop.Expressions;
 using System.Linq.Expressions;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Java.Interop {
 
@@ -246,7 +247,7 @@ public override IList<Boolean> CreateGenericValue (ref JniObjectReference refere
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaBooleanArray (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Boolean> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Boolean> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Boolean>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -257,7 +258,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Boolean> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Boolean> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Boolean>.DestroyArgumentState<JavaBooleanArray> (value, ref state, synchronize);
 			}
@@ -422,7 +423,7 @@ public override IList<SByte> CreateGenericValue (ref JniObjectReference referenc
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaSByteArray (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<SByte> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<SByte> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<SByte>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -433,7 +434,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<SByte> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<SByte> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<SByte>.DestroyArgumentState<JavaSByteArray> (value, ref state, synchronize);
 			}
@@ -598,7 +599,7 @@ public override IList<Char> CreateGenericValue (ref JniObjectReference reference
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaCharArray (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Char> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Char> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Char>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -609,7 +610,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Char> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Char> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Char>.DestroyArgumentState<JavaCharArray> (value, ref state, synchronize);
 			}
@@ -774,7 +775,7 @@ public override IList<Int16> CreateGenericValue (ref JniObjectReference referenc
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaInt16Array (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Int16> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Int16> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Int16>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -785,7 +786,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Int16> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Int16> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Int16>.DestroyArgumentState<JavaInt16Array> (value, ref state, synchronize);
 			}
@@ -950,7 +951,7 @@ public override IList<Int32> CreateGenericValue (ref JniObjectReference referenc
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaInt32Array (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Int32> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Int32> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Int32>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -961,7 +962,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Int32> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Int32> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Int32>.DestroyArgumentState<JavaInt32Array> (value, ref state, synchronize);
 			}
@@ -1126,7 +1127,7 @@ public override IList<Int64> CreateGenericValue (ref JniObjectReference referenc
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaInt64Array (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Int64> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Int64> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Int64>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -1137,7 +1138,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Int64> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Int64> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Int64>.DestroyArgumentState<JavaInt64Array> (value, ref state, synchronize);
 			}
@@ -1302,7 +1303,7 @@ public override IList<Single> CreateGenericValue (ref JniObjectReference referen
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaSingleArray (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Single> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Single> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Single>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -1313,7 +1314,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Single> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Single> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Single>.DestroyArgumentState<JavaSingleArray> (value, ref state, synchronize);
 			}
@@ -1478,7 +1479,7 @@ public override IList<Double> CreateGenericValue (ref JniObjectReference referen
 						(ref JniObjectReference h, JniObjectReferenceOptions o) => new JavaDoubleArray (ref h, o));
 			}
 
-			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState (IList<Double> value, ParameterAttributes synchronize)
+			public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState ([MaybeNull] IList<Double> value, ParameterAttributes synchronize)
 			{
 				return JavaArray<Double>.CreateArgumentState (value, synchronize, (list, copy) => {
 					var a = copy
@@ -1489,7 +1490,7 @@ public override JniValueMarshalerState CreateGenericObjectReferenceArgumentState
 				});
 			}
 
-			public override void DestroyGenericArgumentState (IList<Double> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
+			public override void DestroyGenericArgumentState ([AllowNull] IList<Double> value, ref JniValueMarshalerState state, ParameterAttributes synchronize)
 			{
 				JavaArray<Double>.DestroyArgumentState<JavaDoubleArray> (value, ref state, synchronize);
 			}

src/Java.Interop/Java.Interop/JavaProxyObject.cs

@@ -1,4 +1,4 @@
-#nullable enable
+#nullable enable
 
 using System;
 using System.Diagnostics.CodeAnalysis;
@@ -51,7 +51,7 @@ public override bool Equals (object? obj)
 
 		public bool Equals (JavaProxyObject? other) => object.Equals (Value, other?.Value);
 
-		public override string ToString ()
+		public override string? ToString ()
 		{
 			return Value.ToString ();
 		}
@@ -63,8 +63,7 @@ public override string ToString ()
 				return null;
 
 			lock (CachedValues) {
-				JavaProxyObject proxy;
-				if (CachedValues.TryGetValue (value, out proxy))
+				if (CachedValues.TryGetValue (value, out var proxy))
 					return proxy;
 				proxy = new JavaProxyObject (value);
 				CachedValues.Add (value, proxy);