diff --git a/linter-4.2/src/TypeScriptLinter.ts b/linter-4.2/src/TypeScriptLinter.ts
index c2a79bc87d4d7350fd3f530e5046ce2534d4d920..2c505db757051a3e4dd420250a54ff685e3784fb 100644
--- a/linter-4.2/src/TypeScriptLinter.ts
+++ b/linter-4.2/src/TypeScriptLinter.ts
@@ -1942,18 +1942,25 @@ export class TypeScriptLinter {
     const ARGUMENT_OF_TYPE_NULL_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE = /^Argument of type 'null' is not assignable to parameter of type '.*'\.$/;
     const ARGUMENT_OF_TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE = /^Argument of type 'undefined' is not assignable to parameter of type '.*'\.$/;
 
+    let inLibCall = this.tsUtils.isLibraryType(this.tsTypeChecker.getTypeAtLocation(callExpr.expression));
+
     const chainCheck = (n: ts.DiagnosticMessageChain): boolean => {
-      if (n.code == TYPE_0_IS_NOT_ASSIGNABLE_TO_TYPE_1_ERROR_CODE &&
-        (n.messageText.match(TYPE_UNKNOWN_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE) ||
-         n.messageText.match(TYPE_NULL_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE) ||
-         n.messageText.match(TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE))) {
-        return false;
+      if (n.code == TYPE_0_IS_NOT_ASSIGNABLE_TO_TYPE_1_ERROR_CODE) {
+        if (n.messageText.match(TYPE_UNKNOWN_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE)) {
+          return false;
+        }
+        if (n.messageText.match(TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE)) {
+          return false;
+        }
+        if (inLibCall && n.messageText.match(TYPE_NULL_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE)) {
+          return false;
+        }
       }
       return n.next == undefined ? true : chainCheck(n.next[0]);
     };
 
     const msgCheck = (msg: string): boolean => {
-      if (this.tsUtils.isLibraryType(this.tsTypeChecker.getTypeAtLocation(callExpr.expression))) {
+      if (inLibCall) {
         const match = msg.match(ARGUMENT_OF_TYPE_NULL_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE) ||
           msg.match(ARGUMENT_OF_TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE);
         return !match;
diff --git a/linter-4.2/test/null_check_calls.ts b/linter-4.2/test/null_check_calls.ts
index 18bcaa037e2ad9769e4af2be55978dc84bed139a..b79ac3409082bfe1f5eff1e2b2d119df6c8af985 100644
--- a/linter-4.2/test/null_check_calls.ts
+++ b/linter-4.2/test/null_check_calls.ts
@@ -37,3 +37,11 @@ function fff(a: Array<number>): void {}
 fff(null);
 ff(null);
 f(null);
+
+
+((a: number) => a)(null);
+(a: null | number) => ((b: number) => b)(a);
+
+function inc(a: number) { return a + 1 }
+function neg2null(x: number) { return x > 0 ? x : null }
+inc(neg2null(-1));
diff --git a/linter-4.2/test/null_check_calls.ts.relax.json b/linter-4.2/test/null_check_calls.ts.relax.json
index 9d5793764dd46a1404fda4ed4c2b2e76e5b0996b..b40e140bace347bfea81d26b7ad363e38c4e7b03 100644
--- a/linter-4.2/test/null_check_calls.ts.relax.json
+++ b/linter-4.2/test/null_check_calls.ts.relax.json
@@ -17,16 +17,27 @@
         {
             "line": 33,
             "column": 12,
-            "problem": "StrictDiagnostic",
-            "suggest": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'.",
-            "rule": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'."
+            "problem": "StrictDiagnostic"
         },
         {
             "line": 37,
             "column": 5,
-            "problem": "StrictDiagnostic",
-            "suggest": "Argument of type 'null' is not assignable to parameter of type 'number[]'.",
-            "rule": "Argument of type 'null' is not assignable to parameter of type 'number[]'."
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 42,
+            "column": 20,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 43,
+            "column": 42,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 47,
+            "column": 5,
+            "problem": "StrictDiagnostic"
         }
     ]
 }
\ No newline at end of file
diff --git a/linter-4.2/test/null_check_calls.ts.strict.json b/linter-4.2/test/null_check_calls.ts.strict.json
index 9d5793764dd46a1404fda4ed4c2b2e76e5b0996b..4b6f2852dd29cd8acf45c216092ffd83f45f3ebb 100644
--- a/linter-4.2/test/null_check_calls.ts.strict.json
+++ b/linter-4.2/test/null_check_calls.ts.strict.json
@@ -14,19 +14,35 @@
         "limitations under the License."
     ],
     "nodes": [
+        {
+            "line": 43,
+            "column": 1,
+            "problem": "LimitedReturnTypeInference"
+        },
         {
             "line": 33,
             "column": 12,
-            "problem": "StrictDiagnostic",
-            "suggest": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'.",
-            "rule": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'."
+            "problem": "StrictDiagnostic"
         },
         {
             "line": 37,
             "column": 5,
-            "problem": "StrictDiagnostic",
-            "suggest": "Argument of type 'null' is not assignable to parameter of type 'number[]'.",
-            "rule": "Argument of type 'null' is not assignable to parameter of type 'number[]'."
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 42,
+            "column": 20,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 43,
+            "column": 42,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 47,
+            "column": 5,
+            "problem": "StrictDiagnostic"
         }
     ]
 }
\ No newline at end of file
diff --git a/linter/src/TypeScriptLinter.ts b/linter/src/TypeScriptLinter.ts
index ea461af04a92274d4da8b40833635b00880d692e..94be3f3bfef8c1cf59d6056100d13e1c765786ce 100644
--- a/linter/src/TypeScriptLinter.ts
+++ b/linter/src/TypeScriptLinter.ts
@@ -1564,18 +1564,25 @@ export class TypeScriptLinter {
     const ARGUMENT_OF_TYPE_NULL_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE = /^Argument of type 'null' is not assignable to parameter of type '.*'\.$/;
     const ARGUMENT_OF_TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE = /^Argument of type 'undefined' is not assignable to parameter of type '.*'\.$/;
 
+    let inLibCall = this.tsUtils.isLibraryType(this.tsTypeChecker.getTypeAtLocation(callExpr.expression));
+
     const chainCheck = (n: ts.DiagnosticMessageChain): boolean => {
-      if (n.code == TYPE_0_IS_NOT_ASSIGNABLE_TO_TYPE_1_ERROR_CODE &&
-        (n.messageText.match(TYPE_UNKNOWN_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE) ||
-         n.messageText.match(TYPE_NULL_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE) ||
-         n.messageText.match(TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE))) {
-        return false;
+      if (n.code == TYPE_0_IS_NOT_ASSIGNABLE_TO_TYPE_1_ERROR_CODE) {
+        if (n.messageText.match(TYPE_UNKNOWN_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE)) {
+          return false;
+        }
+        if (n.messageText.match(TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE)) {
+          return false;
+        }
+        if (inLibCall && n.messageText.match(TYPE_NULL_IS_NOT_ASSIGNABLE_TO_TYPE_1_RE)) {
+          return false;
+        }
       }
       return n.next == undefined ? true : chainCheck(n.next[0]);
     };
 
     const msgCheck = (msg: string): boolean => {
-      if (this.tsUtils.isLibraryType(this.tsTypeChecker.getTypeAtLocation(callExpr.expression))) {
+      if (inLibCall) {
         const match = msg.match(ARGUMENT_OF_TYPE_NULL_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE) ||
           msg.match(ARGUMENT_OF_TYPE_UNDEFINED_IS_NOT_ASSIGNABLE_TO_PARAMETER_OF_TYPE_1_RE);
         return !match;
diff --git a/linter/test/null_check_calls.ts b/linter/test/null_check_calls.ts
index 18bcaa037e2ad9769e4af2be55978dc84bed139a..b79ac3409082bfe1f5eff1e2b2d119df6c8af985 100644
--- a/linter/test/null_check_calls.ts
+++ b/linter/test/null_check_calls.ts
@@ -37,3 +37,11 @@ function fff(a: Array<number>): void {}
 fff(null);
 ff(null);
 f(null);
+
+
+((a: number) => a)(null);
+(a: null | number) => ((b: number) => b)(a);
+
+function inc(a: number) { return a + 1 }
+function neg2null(x: number) { return x > 0 ? x : null }
+inc(neg2null(-1));
diff --git a/linter/test/null_check_calls.ts.relax.json b/linter/test/null_check_calls.ts.relax.json
index 9d5793764dd46a1404fda4ed4c2b2e76e5b0996b..b40e140bace347bfea81d26b7ad363e38c4e7b03 100644
--- a/linter/test/null_check_calls.ts.relax.json
+++ b/linter/test/null_check_calls.ts.relax.json
@@ -17,16 +17,27 @@
         {
             "line": 33,
             "column": 12,
-            "problem": "StrictDiagnostic",
-            "suggest": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'.",
-            "rule": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'."
+            "problem": "StrictDiagnostic"
         },
         {
             "line": 37,
             "column": 5,
-            "problem": "StrictDiagnostic",
-            "suggest": "Argument of type 'null' is not assignable to parameter of type 'number[]'.",
-            "rule": "Argument of type 'null' is not assignable to parameter of type 'number[]'."
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 42,
+            "column": 20,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 43,
+            "column": 42,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 47,
+            "column": 5,
+            "problem": "StrictDiagnostic"
         }
     ]
 }
\ No newline at end of file
diff --git a/linter/test/null_check_calls.ts.strict.json b/linter/test/null_check_calls.ts.strict.json
index 9d5793764dd46a1404fda4ed4c2b2e76e5b0996b..4b6f2852dd29cd8acf45c216092ffd83f45f3ebb 100644
--- a/linter/test/null_check_calls.ts.strict.json
+++ b/linter/test/null_check_calls.ts.strict.json
@@ -14,19 +14,35 @@
         "limitations under the License."
     ],
     "nodes": [
+        {
+            "line": 43,
+            "column": 1,
+            "problem": "LimitedReturnTypeInference"
+        },
         {
             "line": 33,
             "column": 12,
-            "problem": "StrictDiagnostic",
-            "suggest": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'.",
-            "rule": "No overload matches this call.\n  Overload 1 of 2, '(func: Function, ...args: unknown[]): Promise<unknown>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'Function'.\n  Overload 2 of 2, '(group: TaskGroup, priority?: Priority | undefined): Promise<unknown[]>', gave the following error.\n    Argument of type 'null' is not assignable to parameter of type 'TaskGroup'."
+            "problem": "StrictDiagnostic"
         },
         {
             "line": 37,
             "column": 5,
-            "problem": "StrictDiagnostic",
-            "suggest": "Argument of type 'null' is not assignable to parameter of type 'number[]'.",
-            "rule": "Argument of type 'null' is not assignable to parameter of type 'number[]'."
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 42,
+            "column": 20,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 43,
+            "column": 42,
+            "problem": "StrictDiagnostic"
+        },
+        {
+            "line": 47,
+            "column": 5,
+            "problem": "StrictDiagnostic"
         }
     ]
 }
\ No newline at end of file