Skip empty string entries when generating string template expression

#KT-19738 Fixed Target versions 1.2.50

compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java

@@ -875,7 +875,10 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
                     constantValue.append(String.valueOf(compileTimeConstant.getValue()));
                 }
                 else {
-                    result.add(new StringTemplateEntry.Constant(constantValue.toString()));
+                    String accumulatedConstantValue = constantValue.toString();
+                    if (accumulatedConstantValue.length() > 0) {
+                        result.add(new StringTemplateEntry.Constant(accumulatedConstantValue));
+                    }
                     constantValue.setLength(0);
 
                     result.add(new StringTemplateEntry.Expression(entryExpression));

compiler/testData/codegen/bytecodeText/stringOperations/doNotAppendEmptyString.kt

@@ -0,0 +1,3 @@
+fun test(foo: Int) = "${foo}bar"
+
+// 0 LDC ""

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -2557,6 +2557,12 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             runTest("compiler/testData/codegen/bytecodeText/stringOperations/concat.kt");
         }
 
+        @TestMetadata("doNotAppendEmptyString.kt")
+        public void testDoNotAppendEmptyString() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/stringOperations/doNotAppendEmptyString.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("interpolation.kt")
         public void testInterpolation() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/stringOperations/interpolation.kt");