Make getters and setters null-safety consistent

This commit ensure that null-safety is consistent between
getters and setters in order to be able to provide beans
with properties with a common type when type safety is
taken in account like with Kotlin.

It also add a few missing property level @Nullable
annotations.

Issue: SPR-15792

spring-test/src/main/java/org/springframework/mock/web/HeaderValueHolder.java

@@ -39,9 +39,11 @@ class HeaderValueHolder {
 	private final List<Object> values = new LinkedList<>();
 
 
-	public void setValue(Object value) {
+	public void setValue(@Nullable Object value) {
 		this.values.clear();
-		this.values.add(value);
+		if (value != null) {
+			this.values.add(value);
+		}
 	}
 
 	public void addValue(Object value) {

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletRequest.java

@@ -917,7 +917,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		return this.asyncSupported;
 	}
 
-	public void setAsyncContext(MockAsyncContext asyncContext) {
+	public void setAsyncContext(@Nullable MockAsyncContext asyncContext) {
 		this.asyncContext = asyncContext;
 	}
 
@@ -941,7 +941,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	// HttpServletRequest interface
 	// ---------------------------------------------------------------------
 
-	public void setAuthType(String authType) {
+	public void setAuthType(@Nullable String authType) {
 		this.authType = authType;
 	}
 
@@ -1102,7 +1102,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		}
 	}
 
-	public void setMethod(String method) {
+	public void setMethod(@Nullable String method) {
 		this.method = method;
 	}
 
@@ -1167,7 +1167,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 				((MockServletContext) this.servletContext).getDeclaredRoles().contains(role)));
 	}
 
-	public void setUserPrincipal(Principal userPrincipal) {
+	public void setUserPrincipal(@Nullable Principal userPrincipal) {
 		this.userPrincipal = userPrincipal;
 	}
 
@@ -1177,7 +1177,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		return this.userPrincipal;
 	}
 
-	public void setRequestedSessionId(String requestedSessionId) {
+	public void setRequestedSessionId(@Nullable String requestedSessionId) {
 		this.requestedSessionId = requestedSessionId;
 	}
 
@@ -1187,7 +1187,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		return this.requestedSessionId;
 	}
 
-	public void setRequestURI(String requestURI) {
+	public void setRequestURI(@Nullable String requestURI) {
 		this.requestURI = requestURI;
 	}
 

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java

@@ -642,7 +642,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 	// Methods for MockRequestDispatcher
 	//---------------------------------------------------------------------
 
-	public void setForwardedUrl(String forwardedUrl) {
+	public void setForwardedUrl(@Nullable String forwardedUrl) {
 		this.forwardedUrl = forwardedUrl;
 	}
 

spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java

@@ -582,7 +582,7 @@ public class MockServletContext implements ServletContext {
 	}
 
 	// @Override - but only against Servlet 4.0
-	public void setRequestCharacterEncoding(String requestCharacterEncoding) {
+	public void setRequestCharacterEncoding(@Nullable String requestCharacterEncoding) {
 		this.requestCharacterEncoding = requestCharacterEncoding;
 	}
 
@@ -593,7 +593,7 @@ public class MockServletContext implements ServletContext {
 	}
 
 	// @Override - but only against Servlet 4.0
-	public void setResponseCharacterEncoding(String responseCharacterEncoding) {
+	public void setResponseCharacterEncoding(@Nullable String responseCharacterEncoding) {
 		this.responseCharacterEncoding = responseCharacterEncoding;
 	}
 

spring-test/src/main/java/org/springframework/test/web/servlet/DefaultMvcResult.java

@@ -76,7 +76,7 @@ class DefaultMvcResult implements MvcResult {
 		return this.mockResponse;
 	}
 
-	public void setHandler(Object handler) {
+	public void setHandler(@Nullable Object handler) {
 		this.handler = handler;
 	}