diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java b/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java
index 54275a974e4..cf135d08ed2 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java
@@ -77,7 +77,6 @@ import org.springframework.expression.spel.ast.Ternary;
 import org.springframework.expression.spel.ast.TypeReference;
 import org.springframework.expression.spel.ast.VariableReference;
 import org.springframework.lang.Nullable;
-import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -137,12 +136,13 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 			this.tokenStreamPointer = 0;
 			this.constructedNodes.clear();
 			SpelNodeImpl ast = eatExpression();
-			Assert.state(ast != null, "No node");
+			if (ast == null) {
+				throw new SpelParseException(this.expressionString, 0, SpelMessage.OOD);
+			}
 			Token t = peekToken();
 			if (t != null) {
-				throw new SpelParseException(t.startPos, SpelMessage.MORE_INPUT, toString(nextToken()));
+				throw new SpelParseException(this.expressionString, t.startPos, SpelMessage.MORE_INPUT, toString(nextToken()));
 			}
-			Assert.isTrue(this.constructedNodes.isEmpty(), "At least one node expected");
 			return new SpelExpression(expressionString, ast, this.configuration);
 		}
 		catch (InternalParseException ex) {
@@ -254,20 +254,20 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 				if (tk == TokenKind.EQ) {
 					return new OpEQ(t.startPos, t.endPos, expr, rhExpr);
 				}
-				Assert.isTrue(tk == TokenKind.NE, "Not-equals token expected");
-				return new OpNE(t.startPos, t.endPos, expr, rhExpr);
+				if (tk == TokenKind.NE) {
+					return new OpNE(t.startPos, t.endPos, expr, rhExpr);
+				}
 			}
 
 			if (tk == TokenKind.INSTANCEOF) {
 				return new OperatorInstanceof(t.startPos, t.endPos, expr, rhExpr);
 			}
-
 			if (tk == TokenKind.MATCHES) {
 				return new OperatorMatches(this.patternCache, t.startPos, t.endPos, expr, rhExpr);
 			}
-
-			Assert.isTrue(tk == TokenKind.BETWEEN, "Between token expected");
-			return new OperatorBetween(t.startPos, t.endPos, expr, rhExpr);
+			if (tk == TokenKind.BETWEEN) {
+				return new OperatorBetween(t.startPos, t.endPos, expr, rhExpr);
+			}
 		}
 		return expr;
 	}
@@ -304,8 +304,7 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 			else if (t.kind == TokenKind.DIV) {
 				expr = new OpDivide(t.startPos, t.endPos, expr, rhExpr);
 			}
-			else {
-				Assert.isTrue(t.kind == TokenKind.MOD, "Mod token expected");
+			else if (t.kind == TokenKind.MOD) {
 				expr = new OpModulus(t.startPos, t.endPos, expr, rhExpr);
 			}
 		}
@@ -335,18 +334,21 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	// unaryExpression: (PLUS^ | MINUS^ | BANG^ | INC^ | DEC^) unaryExpression | primaryExpression ;
 	@Nullable
 	private SpelNodeImpl eatUnaryExpression() {
-		if (peekToken(TokenKind.PLUS, TokenKind.MINUS, TokenKind.NOT)) {
+		if (peekToken(TokenKind.NOT, TokenKind.PLUS, TokenKind.MINUS)) {
 			Token t = takeToken();
 			SpelNodeImpl expr = eatUnaryExpression();
-			Assert.state(expr != null, "No node");
+			if (expr == null) {
+				throw internalException(t.startPos, SpelMessage.OOD);
+			}
 			if (t.kind == TokenKind.NOT) {
 				return new OperatorNot(t.startPos, t.endPos, expr);
 			}
 			if (t.kind == TokenKind.PLUS) {
 				return new OpPlus(t.startPos, t.endPos, expr);
 			}
-			Assert.isTrue(t.kind == TokenKind.MINUS, "Minus token expected");
-			return new OpMinus(t.startPos, t.endPos, expr);
+			if (t.kind == TokenKind.MINUS) {
+				return new OpMinus(t.startPos, t.endPos, expr);
+			}
 		}
 		if (peekToken(TokenKind.INC, TokenKind.DEC)) {
 			Token t = takeToken();
@@ -354,7 +356,9 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 			if (t.getKind() == TokenKind.INC) {
 				return new OpInc(t.startPos, t.endPos, false, expr);
 			}
-			return new OpDec(t.startPos, t.endPos, false, expr);
+			if (t.kind == TokenKind.DEC) {
+				return new OpDec(t.startPos, t.endPos, false, expr);
+			}
 		}
 		return eatPrimaryExpression();
 	}
@@ -414,7 +418,6 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 			return pop();
 		}
 		if (peekToken() == null) {
-			// unexpectedly ran out of data
 			throw internalException(t.startPos, SpelMessage.OOD);
 		}
 		else {
@@ -460,8 +463,7 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 
 	private void eatConstructorArgs(List<SpelNodeImpl> accumulatedArguments) {
 		if (!peekToken(TokenKind.LPAREN)) {
-			throw new InternalParseException(new SpelParseException(this.expressionString,
-					positionOf(peekToken()), SpelMessage.MISSING_CONSTRUCTOR_ARGS));
+			throw internalException(positionOf(peekToken()), SpelMessage.MISSING_CONSTRUCTOR_ARGS);
 		}
 		consumeArguments(accumulatedArguments);
 		eatToken(TokenKind.RPAREN);
@@ -472,7 +474,9 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	 */
 	private void consumeArguments(List<SpelNodeImpl> accumulatedArguments) {
 		Token t = peekToken();
-		Assert.state(t != null, "Expected token");
+		if (t == null) {
+			return;
+		}
 		int pos = t.startPos;
 		Token next;
 		do {
@@ -575,8 +579,7 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	private boolean maybeEatTypeReference() {
 		if (peekToken(TokenKind.IDENTIFIER)) {
 			Token typeName = peekToken();
-			Assert.state(typeName != null, "Expected token");
-			if (!"T".equals(typeName.stringValue())) {
+			if (typeName == null || !"T".equals(typeName.stringValue())) {
 				return false;
 			}
 			// It looks like a type reference but is T being used as a map key?
@@ -605,8 +608,7 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	private boolean maybeEatNullReference() {
 		if (peekToken(TokenKind.IDENTIFIER)) {
 			Token nullToken = peekToken();
-			Assert.state(nullToken != null, "Expected token");
-			if (!"null".equalsIgnoreCase(nullToken.stringValue())) {
+			if (nullToken == null || !"null".equalsIgnoreCase(nullToken.stringValue())) {
 				return false;
 			}
 			nextToken();
@@ -619,12 +621,13 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	//projection: PROJECT^ expression RCURLY!;
 	private boolean maybeEatProjection(boolean nullSafeNavigation) {
 		Token t = peekToken();
-		if (!peekToken(TokenKind.PROJECT, true)) {
+		if (t == null || !peekToken(TokenKind.PROJECT, true)) {
 			return false;
 		}
-		Assert.state(t != null, "No token");
 		SpelNodeImpl expr = eatExpression();
-		Assert.state(expr != null, "No node");
+		if (expr == null) {
+			throw internalException(t.startPos, SpelMessage.OOD);
+		}
 		eatToken(TokenKind.RSQUARE);
 		this.constructedNodes.push(new Projection(nullSafeNavigation, t.startPos, t.endPos, expr));
 		return true;
@@ -634,15 +637,13 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	// map  = LCURLY (key ':' value (COMMA key ':' value)*) RCURLY
 	private boolean maybeEatInlineListOrMap() {
 		Token t = peekToken();
-		if (!peekToken(TokenKind.LCURLY, true)) {
+		if (t == null || !peekToken(TokenKind.LCURLY, true)) {
 			return false;
 		}
-		Assert.state(t != null, "No token");
 		SpelNodeImpl expr = null;
 		Token closingCurly = peekToken();
-		if (peekToken(TokenKind.RCURLY, true)) {
+		if (closingCurly != null && peekToken(TokenKind.RCURLY, true)) {
 			// empty list '{}'
-			Assert.state(closingCurly != null, "No token");
 			expr = new InlineList(t.startPos, closingCurly.endPos);
 		}
 		else if (peekToken(TokenKind.COLON, true)) {
@@ -695,12 +696,13 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 
 	private boolean maybeEatIndexer() {
 		Token t = peekToken();
-		if (!peekToken(TokenKind.LSQUARE, true)) {
+		if (t == null || !peekToken(TokenKind.LSQUARE, true)) {
 			return false;
 		}
-		Assert.state(t != null, "No token");
 		SpelNodeImpl expr = eatExpression();
-		Assert.state(expr != null, "No node");
+		if (expr == null) {
+			throw internalException(t.startPos, SpelMessage.MISSING_SELECTION_EXPRESSION);
+		}
 		eatToken(TokenKind.RSQUARE);
 		this.constructedNodes.push(new Indexer(t.startPos, t.endPos, expr));
 		return true;
@@ -708,10 +710,9 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 
 	private boolean maybeEatSelection(boolean nullSafeNavigation) {
 		Token t = peekToken();
-		if (!peekSelectToken()) {
+		if (t == null || !peekSelectToken()) {
 			return false;
 		}
-		Assert.state(t != null, "No token");
 		nextToken();
 		SpelNodeImpl expr = eatExpression();
 		if (expr == null) {
@@ -889,9 +890,14 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 	//parenExpr : LPAREN! expression RPAREN!;
 	private boolean maybeEatParenExpression() {
 		if (peekToken(TokenKind.LPAREN)) {
-			nextToken();
+			Token t = nextToken();
+			if (t == null) {
+				return false;
+			}
 			SpelNodeImpl expr = eatExpression();
-			Assert.state(expr != null, "No node");
+			if (expr == null) {
+				throw internalException(t.startPos, SpelMessage.OOD);
+			}
 			eatToken(TokenKind.RPAREN);
 			push(expr);
 			return true;
diff --git a/spring-expression/src/test/java/org/springframework/expression/spel/standard/SpelParserTests.java b/spring-expression/src/test/java/org/springframework/expression/spel/standard/SpelParserTests.java
index 33b6e7298e2..bccc0a5b8c2 100644
--- a/spring-expression/src/test/java/org/springframework/expression/spel/standard/SpelParserTests.java
+++ b/spring-expression/src/test/java/org/springframework/expression/spel/standard/SpelParserTests.java
@@ -39,7 +39,9 @@ import static org.springframework.expression.spel.SpelMessage.NON_TERMINATING_DO
 import static org.springframework.expression.spel.SpelMessage.NON_TERMINATING_QUOTED_STRING;
 import static org.springframework.expression.spel.SpelMessage.NOT_AN_INTEGER;
 import static org.springframework.expression.spel.SpelMessage.NOT_A_LONG;
+import static org.springframework.expression.spel.SpelMessage.OOD;
 import static org.springframework.expression.spel.SpelMessage.REAL_CANNOT_BE_LONG;
+import static org.springframework.expression.spel.SpelMessage.RIGHT_OPERAND_PROBLEM;
 import static org.springframework.expression.spel.SpelMessage.RUN_OUT_OF_ARGUMENTS;
 import static org.springframework.expression.spel.SpelMessage.UNEXPECTED_DATA_AFTER_DOT;
 import static org.springframework.expression.spel.SpelMessage.UNEXPECTED_ESCAPE_CHAR;
@@ -76,8 +78,8 @@ class SpelParserTests {
 
 	private static void assertNullOrEmptyExpressionIsRejected(ThrowingCallable throwingCallable) {
 		assertThatIllegalArgumentException()
-			.isThrownBy(throwingCallable)
-			.withMessage("'expressionString' must not be null or blank");
+				.isThrownBy(throwingCallable)
+				.withMessage("'expressionString' must not be null or blank");
 	}
 
 	@Test
@@ -152,7 +154,13 @@ class SpelParserTests {
 		assertParseException(() -> parser.parseRaw("new String(3"), RUN_OUT_OF_ARGUMENTS, 10);
 		assertParseException(() -> parser.parseRaw("new String("), RUN_OUT_OF_ARGUMENTS, 10);
 		assertParseException(() -> parser.parseRaw("\"abc"), NON_TERMINATING_DOUBLE_QUOTED_STRING, 0);
+		assertParseException(() -> parser.parseRaw("abc\""), NON_TERMINATING_DOUBLE_QUOTED_STRING, 3);
 		assertParseException(() -> parser.parseRaw("'abc"), NON_TERMINATING_QUOTED_STRING, 0);
+		assertParseException(() -> parser.parseRaw("abc'"), NON_TERMINATING_QUOTED_STRING, 3);
+		assertParseException(() -> parser.parseRaw("("), OOD, 0);
+		assertParseException(() -> parser.parseRaw(")"), OOD, 0);
+		assertParseException(() -> parser.parseRaw("+"), OOD, 0);
+		assertParseException(() -> parser.parseRaw("1+"), RIGHT_OPERAND_PROBLEM, 1);
 	}
 
 	@Test
@@ -377,7 +385,7 @@ class SpelParserTests {
 
 	private void checkNumberError(String expression, SpelMessage expectedMessage) {
 		assertParseExceptionThrownBy(() -> parser.parseRaw(expression))
-			.satisfies(ex -> assertThat(ex.getMessageCode()).isEqualTo(expectedMessage));
+				.satisfies(ex -> assertThat(ex.getMessageCode()).isEqualTo(expectedMessage));
 	}
 
 	private static ThrowableAssertAlternative<SpelParseException> assertParseExceptionThrownBy(ThrowingCallable throwingCallable) {
@@ -386,15 +394,18 @@ class SpelParserTests {
 
 	private static void assertParseException(ThrowingCallable throwingCallable, SpelMessage expectedMessage, int expectedPosition) {
 		assertParseExceptionThrownBy(throwingCallable)
-			.satisfies(parseExceptionRequirements(expectedMessage, expectedPosition));
+				.satisfies(parseExceptionRequirements(expectedMessage, expectedPosition));
 	}
 
 	private static <E extends SpelParseException> Consumer<E> parseExceptionRequirements(
 			SpelMessage expectedMessage, int expectedPosition) {
+
 		return ex -> {
 			assertThat(ex.getMessageCode()).isEqualTo(expectedMessage);
 			assertThat(ex.getPosition()).isEqualTo(expectedPosition);
-			assertThat(ex.getMessage()).contains(ex.getExpressionString());
+			if (ex.getExpressionString() != null) {
+				assertThat(ex.getMessage()).contains(ex.getExpressionString());
+			}
 		};
 	}